From time to time, a government decides to change its daylight saving time rules. It might stay on daylight time all year, stop changing the clocks, or move the date of the change. When that happens, Hebcal’s candle-lighting and Havdalah times need to be recalculated. This change often takes a few weeks to implement.
Where does Hebcal get time zone information?
Every location on Hebcal, whether you search by ZIP code or city, is linked to a time zone such as America/New_York or Asia/Jerusalem. The rules for each time zone, including when daylight saving time begins and ends, come from the IANA time zone database. This is the same open-source database used by nearly every computer, phone and website in the world.
Hebcal first calculates sunset as a moment in time, and then uses those time zone rules to show it on your local clock. So the sunset calculation itself doesn’t change when the clocks do. Only the time displayed changes.
How long does it take for Hebcal to update?
When a government announces a change, here’s what usually happens:
- Volunteers who maintain the IANA time zone database publish an update.
- That update makes its way into the software Hebcal runs on, in particular Debian Linux and Node.js.
- We update Hebcal’s servers with the new version.
This usually takes a few weeks. If a government announces a change on short notice, it can happen faster. If you notice a problem close to the date of a change, it may simply be that the updated data isn’t available yet.
Do I need to do anything?
- If you subscribed to a Hebcal calendar, no. Your calendar will update on its own after the fix. Calendar apps check for updates about once a day, though Google Calendar can take a bit longer.
- If you downloaded a file or printed a calendar, yes. Those don’t update. Please download or print a new copy after the change takes effect.
A note about Arizona
Most of Arizona doesn’t observe daylight saving time, but the Navajo Nation in northeastern Arizona does. Hebcal uses the time zone that matches each ZIP code or city, so if your times look an hour off in Arizona, please double-check that you entered the right location.
My times look exactly one hour off
A time that is off by exactly one hour almost always points to a time zone problem rather than a sunset calculation problem. A few things to check:
- Make sure your computer or phone is set to the right time zone.
- If you use Outlook on Windows, check that Outlook’s time zone matches your computer’s. A mismatch can shift events by an hour or more (see Outlook all-day events shift when changing time zone).
- Compare with the times shown on Hebcal’s Shabbat times page for your location.
If the times on Hebcal.com itself are off, please contact us with your ZIP code or city, a screenshot, and which calendar app you use. We’ll look into it right away.