Milestone 1.

app/utils/time.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+
+
+def now_iso_utc() -> str:
+    return datetime.now(timezone.utc).replace(microsecond=0).isoformat().replace("+00:00", "Z")
+
+
+def is_iso_utc(value: str) -> bool:
+    try:
+        # Accept the 'Z' suffix
+        if value.endswith("Z"):
+            datetime.fromisoformat(value.replace("Z", "+00:00"))
+        else:
+            datetime.fromisoformat(value)
+        return True
+    except Exception:
+        return False