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A cron expression does not specify a time zone. It specifies calendar fields that a particular scheduler interprets in its effective time zone. If you convert a local run time to one UTC hour and repeat it year-round, it will stop matching that local hour when the region’s UTC offset changes. The right fix depends on whether the job must run at a fixed global instant or at a fixed local wall-clock time.
What a cron time means
0 9 * * * means “at minute 0 of hour 9” in the scheduler’s effective time zone. It does not inherently mean 9 a.m. UTC or 9 a.m. in your own time zone. That zone comes from the scheduler and its configuration.
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A regional zone such as America/New_York represents civil-time rules that can change with daylight saving time (DST) and legal decisions. It is not a permanent UTC offset. A fixed offset such as UTC−5 cannot represent every season—or necessarily future rules—in that region.
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Choose between a fixed instant and a fixed local hour
Use UTC for a globally anchored run
If the job must run at the same instant worldwide, schedule it in UTC. UTC does not shift for DST, so its local-clock display can move when a region changes its offset. That is expected when the requirement is a fixed global instant.
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- 【Have to Plug-in】It's NOT battery operated. It must work with 5V power adapter and 10.5FT cable cord (included). There's a memory battery inside so it will remember your setting even it's disconnected.
Use a named regional zone for a local commitment
If the job must run at, for example, 09:00 every day in New York, use a named zone such as America/New_York on a scheduler that supports it. The scheduler can then apply that region’s time-zone rules. Its behavior at skipped or repeated times still depends on the product’s policy, and its time-zone data must be current.
Convert one-time events by date
For a one-time event, convert the particular date and local time—not just the hour—and verify the resulting UTC instant and weekday. Check whether the chosen local time is ambiguous or nonexistent during a clock change.
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What happens when DST skips or repeats a time
When clocks move forward, some local times do not occur. When clocks move back, some local times occur twice. A schedule at one of those times needs a product-specific outcome; there is no universal “cron” rule.
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| Scheduler or documentation | Documented time-zone behavior | DST transition behavior |
|---|---|---|
Linux crontab(5) |
Supports crontab-level CRON_TZ; schedule fields are interpreted in that zone. |
Its documentation says nonexistent times do not match, while matching times that occur more than once can run twice. Linux crontab(5) |
Linux cron daemon, cron(8) |
Daemon behavior is distinct from the crontab schedule-field description. | For small clock changes, the daemon documents special handling: a specific-time job missed during a forward adjustment can run immediately, and a duplicate run is avoided after a backward adjustment. Identify the actual daemon and version. Linux cron(8) |
| Kubernetes CronJob | Uses .spec.timeZone when set; otherwise the kube-controller-manager’s local time zone applies. The time-zone feature has been stable since Kubernetes v1.27. |
The cited CronJob documentation establishes the configuration and default, not a universal transition policy. Kubernetes CronJob documentation |
| AWS EventBridge Scheduler | Accepts UTC or a selected time zone; UTC is the default when no zone is specified. It uses the IANA time-zone database. | On a spring-forward shift, a scheduled nonexistent date and time is skipped; on a fall-back shift, the schedule runs once, not twice. DST adjustments do not apply to UTC schedules. AWS EventBridge Scheduler schedule types |
| AWS CloudWatch alarm-mute schedule API | The cited API defaults to UTC when the time zone is omitted. | Do not assume this API’s default applies to other AWS scheduling products. AWS CloudWatch Schedule API |
These differences are why a working expression cannot be moved between products on syntax alone: the effective zone, cron dialect, and transition policy may all differ.
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WallarGe 14.5'' Large Digital Wall Clock Battery Operated
- Large Digital Wall Clock with Big Numbers - Easy to Read: WallarGe digital wall clock has a high-definition LCD screen measures 14x6 inch and the time display is 8.1x4.3 inch, the large display helps you read the time from many angles at a room distance. You can also read the indoor temperature and date on screen for full information
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- Wall Clock Large Display with AUTO DST: The clock will automatically adjust time in Daylight Saving Time with AUTO DST on. It has two time display modes (Military time and Standard time), just click 12/24 button to switch. And the alarm is optional, it can be turned off manually if for no need
Trace the schedule’s effective time zone
- Identify the scheduler and version. Confirm whether the job runs under a Linux cron daemon, a Kubernetes CronJob, AWS EventBridge Scheduler, or another service. Documentation for one product is not a guarantee about another.
- For Linux, inspect both system and crontab settings. Check the host’s
/etc/localtimeand look forCRON_TZin the relevant crontab.CRON_TZcontrols that crontab’s schedule; log timestamps use the daemon’s local zone. See localtime(5) and ctime(3) for system-zone context. - For Kubernetes, inspect the CronJob manifest. Check
.spec.timeZone. If it is omitted, the kube-controller-manager’s local zone is used. - For AWS, identify the exact scheduling feature. EventBridge Scheduler supports a selected zone. The cited CloudWatch alarm-mute schedule API defaults to UTC if no zone is provided; that is not a general AWS default.
- Check a normal date and both transition dates. Verify the desired local hour on an ordinary week, then confirm what the product does at the next spring-forward and fall-back transitions.
- Keep time-zone rules current. Regional authorities can change their rules, so a named zone only helps when the scheduler’s time-zone data is up to date.
How to compare schedulers for cron time-zone support
Before choosing or migrating a scheduler, compare the behavior that affects the job—not just whether it accepts a familiar cron expression.
- Can you set an explicit named regional time zone?
- What zone applies if you do not set one?
- Does a nonexistent spring-forward time get skipped, caught up, or handled another way?
- Does a repeated fall-back time run once or twice?
- How is the scheduler’s time-zone database supplied and updated?
- Does its cron dialect match the expression being migrated?
For example, Kubernetes exposes .spec.timeZone, AWS EventBridge Scheduler accepts an explicit IANA zone and documents DST handling, and Linux cron documents CRON_TZ while its daemon can have separate clock-change handling. Check each implementation’s own documentation before relying on a particular outcome.
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Digital Wall Clock, Digital Clock Large Display with Remote Control, Corded LED Alarm Clocks with Date, Week, Temp, Humidity, Auto DST, Countdown, for Living Room Bedroom Classroom Office (Blue)
- 【Large LED Display】The 11" corded wall clock features full-screen time display and large bright numbers, easy to read. Here are all the features that you might expect for a digital wall clock: Time, Date, Week, Temp or Humidity. ATTENTION: Must be plugged in to work. Not battery operated.
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