diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 5fa644b7..91b16ab8 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -1,8 +1,9 @@
 on:
   push:
-    branches: [main]
+    branches: [time-feature]
   pull_request:
     branches: [main]
+  workflow_dispatch: 
 
 jobs:
   tests:
diff --git a/src/GC.zig b/src/GC.zig
index 2b4b1ee1..54009aa8 100644
--- a/src/GC.zig
+++ b/src/GC.zig
@@ -463,12 +463,6 @@ fn freeObj(self: *GC, obj: *o.Obj) (std.mem.Allocator.Error || std.fmt.BufPrintE
         },
         .UpValue => {
             const obj_upvalue = o.ObjUpValue.cast(obj).?;
-            if (obj_upvalue.closed) |value| {
-                if (value.isObj()) {
-                    try freeObj(self, value.obj());
-                }
-            }
-
             free(self, o.ObjUpValue, obj_upvalue);
         },
         .Closure => {
diff --git a/src/buzz_api.zig b/src/buzz_api.zig
index 9b856686..08c894f3 100644
--- a/src/buzz_api.zig
+++ b/src/buzz_api.zig
@@ -775,6 +775,9 @@ export fn bz_newQualifiedObjectInstance(self: *VM, qualified_name: [*]const u8,
         @panic("Could not create error");
     };
 
+    // Keep the new instance rooted while cloning defaults may allocate.
+    self.push(instance.toValue());
+
     // Set instance fields with default values
     for (object.defaults, 0..) |default, idx| {
         if (default) |udefault| {
@@ -786,7 +789,7 @@ export fn bz_newQualifiedObjectInstance(self: *VM, qualified_name: [*]const u8,
         }
     }
 
-    return instance.toValue();
+    return self.pop();
 }
 
 fn instanciateError(
@@ -890,6 +893,9 @@ export fn bz_newObjectInstance(vm: *VM, object_value: v.Value, typedef_value: v.
         ) catch @panic("Out of memory"),
     ) catch @panic("Could not instanciate object");
 
+    // Keep the new instance rooted while cloning defaults may allocate.
+    vm.push(instance.toValue());
+
     // If not anonymous, set default fields
     if (object) |uobject| {
         for (uobject.defaults, 0..) |default, idx| {
@@ -903,7 +909,7 @@ export fn bz_newObjectInstance(vm: *VM, object_value: v.Value, typedef_value: v.
         }
     }
 
-    return instance.toValue();
+    return vm.pop();
 }
 
 export fn bz_getObjectField(object_value: v.Value, field_idx: usize) callconv(.c) v.Value {
diff --git a/src/lib/buzz_time.zig b/src/lib/buzz_time.zig
new file mode 100644
index 00000000..8497af90
--- /dev/null
+++ b/src/lib/buzz_time.zig
@@ -0,0 +1,32 @@
+const api = @import("buzz_api.zig");
+const std = @import("std");
+
+pub export fn timeNow(ctx: *api.NativeCtx) callconv(.c) c_int {
+    const ts = std.Io.Timestamp.now(ctx.getIo(), .real);
+    const ms = ts.toMilliseconds();
+    ctx.vm.bz_push(.fromDouble(@floatFromInt(ms)));
+    return 1;
+}
+
+pub export fn timeMonotonic(ctx: *api.NativeCtx) callconv(.c) c_int {
+    const ts = std.Io.Timestamp.now(ctx.getIo(), .awake);
+    const ms = ts.toMilliseconds();
+    ctx.vm.bz_push(.fromDouble(@floatFromInt(ms)));
+    return 1;
+}
+
+pub export fn timeCpu(ctx: *api.NativeCtx) callconv(.c) c_int {
+    const ts = std.Io.Timestamp.now(ctx.getIo(), .cpu_process);
+    const ms = ts.toMilliseconds();
+    ctx.vm.bz_push(.fromDouble(@floatFromInt(ms)));
+    return 1;
+}
+
+pub const library = api.BuzzApi(
+    "time",
+    &.{
+        &.{ "now", timeNow },
+        &.{ "monotonic", timeMonotonic },
+        &.{ "cpu", timeCpu },
+    },
+){};
diff --git a/src/lib/static_headers.zig b/src/lib/static_headers.zig
index 4ece9fa0..905bba89 100644
--- a/src/lib/static_headers.zig
+++ b/src/lib/static_headers.zig
@@ -22,6 +22,7 @@ pub const math = Header{ .name = "math", .path = "math.buzz" };
 pub const os = Header{ .name = "os", .path = "os.buzz" };
 pub const serialize = Header{ .name = "serialize", .path = "serialize.buzz" };
 pub const std = Header{ .name = "std", .path = "std.buzz" };
+pub const time = Header{ .name = "time", .path = "time.buzz" };
 pub const testing = Header{ .name = "test", .path = "testing.buzz" };
 
 /// Buzz headers bundled with the compiler/runtime and installed for tooling.
@@ -41,4 +42,5 @@ pub const all = [_]Header{
     serialize,
     std,
     testing,
+    time,
 };
diff --git a/src/lib/static_libraries.zig b/src/lib/static_libraries.zig
index 6463a3c5..d64f59bb 100644
--- a/src/lib/static_libraries.zig
+++ b/src/lib/static_libraries.zig
@@ -30,6 +30,7 @@ pub const all = [_]Library{
     .{ .header = static_headers.os, .zig_path = "buzz_os.zig", .wasm_native = false },
     .{ .header = static_headers.serialize, .zig_path = "buzz_serialize.zig", .wasm_native = true },
     .{ .header = static_headers.std, .zig_path = "buzz_std.zig", .wasm_native = true },
+    .{ .header = static_headers.time, .zig_path = "buzz_time.zig", .wasm_native = false },
     .{ .header = static_headers.testing, .zig_path = null, .wasm_native = false },
 };
 
@@ -98,6 +99,7 @@ fn nativeMethods(comptime library: Library) std.StaticStringMap(buzz_api.NativeF
     if (std.mem.eql(u8, zig_path, "buzz_os.zig")) return checkedNativeMethods(library, @import("buzz_os.zig").library);
     if (std.mem.eql(u8, zig_path, "buzz_serialize.zig")) return checkedNativeMethods(library, @import("buzz_serialize.zig").library);
     if (std.mem.eql(u8, zig_path, "buzz_std.zig")) return checkedNativeMethods(library, @import("buzz_std.zig").library);
+    if (std.mem.eql(u8, zig_path, "buzz_time.zig")) return checkedNativeMethods(library, @import("buzz_time.zig").library);
 
     @compileError("unknown native library path: " ++ zig_path);
 }
diff --git a/src/lib/time.buzz b/src/lib/time.buzz
new file mode 100644
index 00000000..15d7f98f
--- /dev/null
+++ b/src/lib/time.buzz
@@ -0,0 +1,12 @@
+namespace time;
+
+import "buzz:errors";
+
+/// Real-time (wall-clock) in milliseconds since Unix epoch
+export extern fun now() > double;
+
+/// Monotonic clock in milliseconds (never goes backwards for intervals)
+export extern fun monotonic() > double;
+
+/// Cpu time used by the current process in milliseconds
+export extern fun cpu() > double !> errors\UnexpectedError;
diff --git a/src/obj.zig b/src/obj.zig
index 4a216b0d..c453956c 100644
--- a/src/obj.zig
+++ b/src/obj.zig
@@ -1571,16 +1571,20 @@ pub const ObjObjectInstance = struct {
         type_def: *ObjTypeDef,
         gc: *GC,
     ) !Self {
+        const fields = try gc.allocateMany(
+            Value,
+            type_def.resolved_type.?.ObjectInstance.of
+                .resolved_type.?.Object
+                .propertiesCount(),
+        );
+
+        @memset(fields, Value.Null);
+
         return .{
             .vm = vm,
             .object = object,
             .type_def = type_def,
-            .fields = try gc.allocateMany(
-                Value,
-                type_def.resolved_type.?.ObjectInstance.of
-                    .resolved_type.?.Object
-                    .propertiesCount(),
-            ),
+            .fields = fields,
         };
     }
 
@@ -1759,15 +1763,23 @@ pub const ObjObject = struct {
     property_count: ?usize = 0,
 
     pub fn init(allocator: Allocator, type_def: *ObjTypeDef) !Self {
+        const fields = try allocator.alloc(
+            Value,
+            type_def.resolved_type.?.Object.fields.count(),
+        );
+        errdefer allocator.free(fields);
+
+        const defaults = try allocator.alloc(
+            ?Value,
+            type_def.resolved_type.?.Object.propertiesCount(),
+        );
+
+        @memset(fields, Value.Void);
+        @memset(defaults, null);
+
         const self = Self{
-            .fields = try allocator.alloc(
-                Value,
-                type_def.resolved_type.?.Object.fields.count(),
-            ),
-            .defaults = try allocator.alloc(
-                ?Value,
-                type_def.resolved_type.?.Object.propertiesCount(),
-            ),
+            .fields = fields,
+            .defaults = defaults,
             .type_def = type_def,
         };
 
@@ -5925,24 +5937,38 @@ pub fn cloneObject(obj: *Obj, vm: *VM) !Value {
 
         .List => {
             const list = ObjList.cast(obj).?;
+            var items = try list.items.clone(vm.gc.allocator);
+            errdefer items.deinit(vm.gc.allocator);
+
+            const methods = try vm.gc.allocator.alloc(?*ObjNative, list.methods.len);
+            errdefer vm.gc.allocator.free(methods);
+
+            @memcpy(methods, list.methods);
 
             return (try vm.gc.allocateObject(
                 ObjList{
                     .type_def = list.type_def,
-                    .items = try list.items.clone(vm.gc.allocator),
-                    .methods = list.methods,
+                    .items = items,
+                    .methods = methods,
                 },
             )).toValue();
         },
 
         .Map => {
             const map = ObjMap.cast(obj).?;
+            var cloned_map = try map.map.clone(vm.gc.allocator);
+            errdefer cloned_map.deinit(vm.gc.allocator);
+
+            const methods = try vm.gc.allocator.alloc(?*ObjNative, map.methods.len);
+            errdefer vm.gc.allocator.free(methods);
+
+            @memcpy(methods, map.methods);
 
             return (try vm.gc.allocateObject(
                 ObjMap{
                     .type_def = map.type_def,
-                    .map = try map.map.clone(vm.gc.allocator),
-                    .methods = map.methods,
+                    .map = cloned_map,
+                    .methods = methods,
                 },
             )).toValue();
         },
diff --git a/src/vm.zig b/src/vm.zig
index 23bf3a2b..451fc45f 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -3084,6 +3084,9 @@ pub const VM = struct {
             unreachable;
         };
 
+        // Keep the new instance rooted while cloning defaults may allocate.
+        self.push(obj_instance.toValue());
+
         // If not anonymous, set default fields
         if (object) |uobject| {
             // Set instance fields with default values
@@ -3104,8 +3107,6 @@ pub const VM = struct {
             }
         }
 
-        self.push(obj_instance.toValue());
-
         const frame = self.currentFrame().?;
         const next_full_instruction = self.readInstruction(frame);
         @call(
diff --git a/tests/behavior/c-buzz-api.buzz b/tests/behavior/c-buzz-api.buzz
index 28d23891..f6e11987 100644
--- a/tests/behavior/c-buzz-api.buzz
+++ b/tests/behavior/c-buzz-api.buzz
@@ -1,6 +1,43 @@
 import "buzz:std";
 import "../utils/buzz_c_api";
 
+object ApiDefaultClone {
+    tokens: [int] = [
+        1, 2, 3, 4, 5, 6, 7, 8,
+        9, 10, 11, 12, 13, 14, 15, 16,
+        17, 18, 19, 20, 21, 22, 23, 24,
+        25, 26, 27, 28, 29, 30, 31, 32,
+        33, 34, 35, 36, 37, 38, 39, 40,
+        41, 42, 43, 44, 45, 46, 47, 48,
+        49, 50, 51, 52, 53, 54, 55, 56,
+        57, 58, 59, 60, 61, 62, 63, 64,
+        65, 66, 67, 68, 69, 70, 71, 72,
+        73, 74, 75, 76, 77, 78, 79, 80,
+        81, 82, 83, 84, 85, 86, 87, 88,
+        89, 90, 91, 92, 93, 94, 95, 96,
+        97, 98, 99, 100, 101, 102, 103, 104,
+        105, 106, 107, 108, 109, 110, 111, 112,
+        113, 114, 115, 116, 117, 118, 119, 120,
+        121, 122, 123, 124, 125, 126, 127, 128,
+        129, 130, 131, 132, 133, 134, 135, 136,
+        137, 138, 139, 140, 141, 142, 143, 144,
+        145, 146, 147, 148, 149, 150, 151, 152,
+        153, 154, 155, 156, 157, 158, 159, 160,
+        161, 162, 163, 164, 165, 166, 167, 168,
+        169, 170, 171, 172, 173, 174, 175, 176,
+        177, 178, 179, 180, 181, 182, 183, 184,
+        185, 186, 187, 188, 189, 190, 191, 192,
+        193, 194, 195, 196, 197, 198, 199, 200,
+        201, 202, 203, 204, 205, 206, 207, 208,
+        209, 210, 211, 212, 213, 214, 215, 216,
+        217, 218, 219, 220, 221, 222, 223, 224,
+        225, 226, 227, 228, 229, 230, 231, 232,
+        233, 234, 235, 236, 237, 238, 239, 240,
+        241, 242, 243, 244, 245, 246, 247, 248,
+        249, 250, 251, 252, 253, 254, 255, 256,
+    ],
+}
+
 test "C buzz api library" {
     std\assert(
         buzz_c_api\add(40, rhs: 2) == 42,
@@ -22,4 +59,11 @@ test "C buzz api library" {
         buzz_c_api\argCount(1, b: 2, c: 3) == 3,
         message: "C library can read NativeCtx arg_count"
     );
+    std\assert(
+        buzz_c_api\instantiateDefaultedObject(
+            ApiDefaultClone,
+            typedef_value: typeof ApiDefaultClone{}
+        ) == 5120000,
+        message: "C library can instantiate objects with cloneable defaults under GC pressure"
+    );
 }
diff --git a/tests/behavior/objects.buzz b/tests/behavior/objects.buzz
index dc8df491..250aee44 100644
--- a/tests/behavior/objects.buzz
+++ b/tests/behavior/objects.buzz
@@ -41,3 +41,52 @@ test "Object with static fields" {
 
     std\assert(second.id == Second.nextId, message: "could use static fields");
 }
+
+object CloneDefault {
+    tokens: [int] = [
+        1, 2, 3, 4, 5, 6, 7, 8,
+        9, 10, 11, 12, 13, 14, 15, 16,
+        17, 18, 19, 20, 21, 22, 23, 24,
+        25, 26, 27, 28, 29, 30, 31, 32,
+        33, 34, 35, 36, 37, 38, 39, 40,
+        41, 42, 43, 44, 45, 46, 47, 48,
+        49, 50, 51, 52, 53, 54, 55, 56,
+        57, 58, 59, 60, 61, 62, 63, 64,
+        65, 66, 67, 68, 69, 70, 71, 72,
+        73, 74, 75, 76, 77, 78, 79, 80,
+        81, 82, 83, 84, 85, 86, 87, 88,
+        89, 90, 91, 92, 93, 94, 95, 96,
+        97, 98, 99, 100, 101, 102, 103, 104,
+        105, 106, 107, 108, 109, 110, 111, 112,
+        113, 114, 115, 116, 117, 118, 119, 120,
+        121, 122, 123, 124, 125, 126, 127, 128,
+        129, 130, 131, 132, 133, 134, 135, 136,
+        137, 138, 139, 140, 141, 142, 143, 144,
+        145, 146, 147, 148, 149, 150, 151, 152,
+        153, 154, 155, 156, 157, 158, 159, 160,
+        161, 162, 163, 164, 165, 166, 167, 168,
+        169, 170, 171, 172, 173, 174, 175, 176,
+        177, 178, 179, 180, 181, 182, 183, 184,
+        185, 186, 187, 188, 189, 190, 191, 192,
+        193, 194, 195, 196, 197, 198, 199, 200,
+        201, 202, 203, 204, 205, 206, 207, 208,
+        209, 210, 211, 212, 213, 214, 215, 216,
+        217, 218, 219, 220, 221, 222, 223, 224,
+        225, 226, 227, 228, 229, 230, 231, 232,
+        233, 234, 235, 236, 237, 238, 239, 240,
+        241, 242, 243, 244, 245, 246, 247, 248,
+        249, 250, 251, 252, 253, 254, 255, 256,
+    ],
+}
+
+test "Objects keep cloneable defaults alive during instantiation" {
+    var i = 0;
+    var total = 0;
+
+    while (i < 20000) {
+        total = total + CloneDefault{}.tokens[0];
+        i = i + 1;
+    }
+
+    std\assert(total == 20000, message: "object instances survive GC while cloning defaults");
+}
diff --git a/tests/behavior/time.buzz b/tests/behavior/time.buzz
new file mode 100644
index 00000000..a62c3b60
--- /dev/null
+++ b/tests/behavior/time.buzz
@@ -0,0 +1,31 @@
+import "buzz:std";
+import "buzz:time";
+
+test "now returns a positive number" {
+    final now = time\now();
+    std\assert(
+        now > 0,
+        message: "now should be greater than 0"
+    );
+}
+
+test "monotonic increases" {
+    final start = time\monotonic();
+    os\sleep(10.0);
+    final end = time\monotonic();
+    std\assert(
+        end > start,
+        message: "monotonic should increase after sleep"
+    );
+}
+
+test "cpu returns a positive number" {
+    final cpu = time\cpu() catch {
+        // CPU clock might not be available on all platforms
+        return;
+    };
+    std\assert(
+        cpu >= 0,
+        message: "cpu time should be >= 0"
+    );
+}
diff --git a/tests/behavior/upvalues.buzz b/tests/behavior/upvalues.buzz
index aed8bcaf..4cd49700 100644
--- a/tests/behavior/upvalues.buzz
+++ b/tests/behavior/upvalues.buzz
@@ -1,4 +1,10 @@
 import "buzz:std";
+import "buzz:gc";
+
+enum CapturedEnum {
+    one,
+    two,
+}
 
 fun upvals() > fun () {
     final upvalue = 12;
@@ -10,3 +16,17 @@ fun upvals() > fun () {
 test "Upvalues" {
     upvals()();
 }
+
+fun captureEnumCase() > fun () > CapturedEnum {
+    final captured = CapturedEnum.two;
+
+    return fun () > CapturedEnum => captured;
+}
+
+test "Closed upvalues can capture enum cases through GC" {
+    _ = captureEnumCase();
+
+    gc\collect();
+
+    std\assert(true, message: "collecting discarded closures with enum captures does not corrupt GC");
+}
diff --git a/tests/utils/buzz_c_api.buzz b/tests/utils/buzz_c_api.buzz
index c8133c56..12d8ccda 100644
--- a/tests/utils/buzz_c_api.buzz
+++ b/tests/utils/buzz_c_api.buzz
@@ -5,3 +5,5 @@ export extern fun add(lhs: int, rhs: int) > int;
 export extern fun isNumber(value: any) > bool;
 
 export extern fun argCount(a: int, b: int, c: int) > int;
+
+export extern fun instantiateDefaultedObject(object_value: any, typedef_value: type) > int;
diff --git a/tests/utils/buzz_c_api.c b/tests/utils/buzz_c_api.c
index 388b8a4c..3b6d55ca 100644
--- a/tests/utils/buzz_c_api.c
+++ b/tests/utils/buzz_c_api.c
@@ -23,6 +23,27 @@ static int argCount(NativeCtx *ctx) {
     return 1;
 }
 
+static int instantiateDefaultedObject(NativeCtx *ctx) {
+    Value object_value = bz_peek(ctx->vm, 1);
+    Value typedef_value = bz_peek(ctx->vm, 0);
+    Integer total = 0;
+
+    for (int i = 0; i < 20000; i++) {
+        Value instance = bz_newObjectInstance(
+            ctx->vm,
+            object_value,
+            typedef_value
+        );
+        Value tokens = bz_getObjectInstanceProperty(instance, 0);
+
+        total += (Integer)bz_listLen(tokens);
+    }
+
+    bz_push(ctx->vm, bz_valueFromInteger(total));
+
+    return 1;
+}
+
 NativeFn buzz_c_api(const char *symbol) {
     if (strcmp(symbol, "add") == 0) {
         return add;
@@ -36,5 +57,9 @@ NativeFn buzz_c_api(const char *symbol) {
         return argCount;
     }
 
+    if (strcmp(symbol, "instantiateDefaultedObject") == 0) {
+        return instantiateDefaultedObject;
+    }
+
     return 0;
 }