Fall back to UTC for iot time when the device clock is not set

An unprovisioned device can report a clock far in the past (e.g. year 2000). When its timezone has to be guessed from the offset to the host time, the resulting delta is years long and timezone(offset) raises "offset must be a timedelta strictly between -timedelta(hours=24) and timedelta(hours=24)", which breaks update() and so every cli command. Real UTC offsets range from -12h to +14h, so treat anything beyond that as an unset clock and use UTC instead of guessing. Fixes #1767 Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
rytilahti · Oct 4, 2026 · Sep 25, 2026 · Sep 25, 2026 · 448aca3cd65649774cfc6f9a3dc2d3e3982cabd4
commit 448aca3cd65649774cfc6f9a3dc2d3e3982cabd4
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