diff --git a/build.rs b/build.rs
index 8aab1330d3e8..3845ad1d3ede 100644
--- a/build.rs
+++ b/build.rs
@@ -40,6 +40,9 @@ const ALLOWED_CFGS: &[&str] = &[
     "musl_redir_time64",
     "vxworks_lt_25_09",
     "libc_pauthtest",
+    // Global flag to enable one of `linux_time_bits64` or `gnu_time_bits64`.
+    // The musl flags are enabled by default on supported platforms.
+    "time64",
 ];
 
 // Extra values to allow for check-cfg.
@@ -169,6 +172,9 @@ fn main() {
     // OpenHarmony uses a fork of the musl libc
     let musl = target_env == "musl" || target_env == "ohos";
 
+    // Single entry-point to enable `time64` on supported platforms.
+    let time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_TIME64");
+
     // loongarch64, hexagon, ohos and pauthtest only exist with recent musl
     if target_arch == "loongarch64"
         || target_arch == "hexagon"
@@ -190,7 +196,7 @@ fn main() {
     }
 
     let uclibc_use_time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_UCLIBC_TIME64");
-    if target_env == "uclibc" && uclibc_use_time64 {
+    if target_env == "uclibc" && (uclibc_use_time64 || time64) {
         set_cfg("linux_time_bits64");
     }
 
@@ -230,7 +236,7 @@ fn main() {
             }
         };
 
-        if timebits == "64" {
+        if timebits == "64" || time64 {
             set_cfg("linux_time_bits64");
             set_cfg("gnu_file_offset_bits64");
             set_cfg("gnu_time_bits64");
diff --git a/libc-test/build/main.rs b/libc-test/build/main.rs
index fc05c0df16c1..93afdfdd0904 100755
--- a/libc-test/build/main.rs
+++ b/libc-test/build/main.rs
@@ -724,6 +724,7 @@ fn test_windows(t: &Target) {
     }
     cfg.define("_WIN32_WINNT", Some("0x8000"));
 
+    let time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_TIME64");
     let win_gnu_x86_time64 = match env::var("CARGO_CFG_LIBC_UNSTABLE_GNU_TIME_BITS") {
         Ok(v) if v == "64" => true,
         Ok(v) if v == "32" => false,
@@ -736,7 +737,7 @@ fn test_windows(t: &Target) {
     // Needed for the Windows `time_t` test.
     println!("cargo::rustc-check-cfg=cfg(gnu_time_bits64)");
 
-    if x86_32 && gnu && win_gnu_x86_time64 {
+    if x86_32 && gnu && (win_gnu_x86_time64 || time64) {
         cfg.cfg("gnu_time_bits64", None);
         println!("cargo::rustc-cfg=gnu_time_bits64");
     }
@@ -3830,6 +3831,7 @@ fn config_gnu_bits(t: &Target, cfg: &mut ctest::TestGenerator) {
     if t.gnu() && t.linux() && !t.x32() && !t.riscv32() && t.pointer_width == P32 {
         let defaultbits = "32";
         let mut tb_env = env::var("CARGO_CFG_LIBC_UNSTABLE_GNU_TIME_BITS");
+        let time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_TIME64");
 
         // FIXME: remove these fallbacks in a few releases
         if let Ok(old_tb_env) = env::var("RUST_LIBC_UNSTABLE_GNU_TIME_BITS") {
@@ -3858,7 +3860,7 @@ fn config_gnu_bits(t: &Target, cfg: &mut ctest::TestGenerator) {
             }
         };
 
-        if timebits == "64" {
+        if timebits == "64" || time64 {
             cfg.define("_TIME_BITS", Some("64"));
             cfg.define("_FILE_OFFSET_BITS", Some("64"));
             cfg.cfg("linux_time_bits64", None);
@@ -3923,6 +3925,8 @@ fn test_linux(t: &Target) {
         None => panic!("failed to detect kernel version for Linux target {t:?}",),
     };
 
+    let time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_TIME64");
+
     let mut musl_v1_2 = env_flag("CARGO_CFG_LIBC_UNSTABLE_MUSL_V1_2");
     if musl_v1_2 {
         assert!(musl);
@@ -3949,7 +3953,7 @@ fn test_linux(t: &Target) {
     }
 
     let uclibc_use_time64 = env_flag("CARGO_CFG_LIBC_UNSTABLE_UCLIBC_TIME64");
-    if uclibc && uclibc_use_time64 {
+    if uclibc && (uclibc_use_time64 || time64) {
         cfg.cfg("linux_time_bits64", None);
     }
     cfg.define("_GNU_SOURCE", None)