diff --git a/kasa/iot/modules/time.py b/kasa/iot/modules/time.py
@@ -35,7 +35,7 @@ async def _post_update_hook(self) -> None:
         If the configured zone is not available on this host, compute the device's
         current UTC offset and choose a best-match available zone, preferring DST-
         observing candidates when the original index implies DST. As a last resort,
-        use a fixed-offset timezone.
+        use a fixed-offset timezone. If the device clock is not set, use UTC.
         """
         if res := self.data.get("get_timezone"):
             idx = res.get("index")
@@ -58,6 +58,11 @@ async def _post_update_hook(self) -> None:
             now_utc = datetime.now(UTC)
             delta = device_local - now_utc.replace(tzinfo=None)
             rounded = timedelta(seconds=60 * round(delta.total_seconds() / 60))
+            # UTC offsets range from -12h to +14h, anything beyond that means the
+            # device clock is not set (e.g. before provisioning).
+            if abs(rounded) > timedelta(hours=14):
+                self._timezone = UTC
+                return
 
             dst_expected = None
             if res := self.data.get("get_timezone"):

diff --git a/tests/test_common_modules.py b/tests/test_common_modules.py
@@ -513,6 +513,40 @@ async def test_time_post_update_uses_offset_when_index_missing_unit(
     assert inst.timezone.utcoffset(now) == timedelta(0)
 
 
+@device_iot
+async def test_time_post_update_unsynced_clock_uses_utc(
+    dev: Device, mocker: MockerFixture
+):
+    """Fall back to UTC when the device clock is not set.
+
+    An unprovisioned device can report e.g. year 2000, which is no valid UTC offset
+    away from the host time, so the offset-based guess must not be attempted.
+    """
+    from zoneinfo import ZoneInfoNotFoundError
+
+    proto = dev.protocol._transport.proto  # type: ignore[attr-defined]
+    for target in ("time", "smartlife.iot.common.timesetting"):
+        if target in proto:
+            proto[target]["get_time"] = {
+                "year": 2000,
+                "month": 1,
+                "mday": 1,
+                "hour": 2,
+                "min": 45,
+                "sec": 0,
+            }
+    # Force the offset-based path, as when the zone is not available on the host
+    mocker.patch(
+        "kasa.iot.modules.time.get_timezone",
+        new=AsyncMock(side_effect=ZoneInfoNotFoundError("missing on host")),
+    )
+
+    await dev.update()
+    time_mod = dev.modules[Module.Time]
+    assert time_mod.timezone is UTC
+    assert time_mod.time.year == 2000
+
+
 async def test_time_get_time_exception_returns_none_unit(mocker: MockerFixture):
     """Cover Time.get_time exception path (unit test of iot Time)."""
     from kasa.iot.modules.time import Time as TimeModule