Time zones change twice a year in most of the United States, and your device must update automatically or you will miss security patches and software updates
In the United States, daylight saving time begins on the second Sunday in March at 2 a.m. local time, and ends on the first Sunday in November at 2 a.m. local time. When the change happens, your device's clock jumps forward one hour in spring and back one hour in fall. If your device does not update its time zone rules automatically, it will be off by an hour, which breaks the timestamps on security certificates, delays patch installations, and can lock you out of accounts that use time-based authentication.
Not every place in the United States observes daylight saving time. Hawaii, most of Arizona, and U.S. territories like Puerto Rico and Guam do not change their clocks. If you live in or travel to one of these places, your device needs to know that, or it will explore the wrong time zone rules and cause the same problems.
Key Takeaways
- Daylight saving time in the U.S. starts the second Sunday in March and ends the first Sunday in November, and your device must update its clock automatically or security features will fail.
- If your device's time is wrong by even one hour, security certificates will show as invalid, updates will not install, and two-factor authentication codes will not work.
- Hawaii, most of Arizona, Puerto Rico, Guam, and the U.S. Virgin Islands do not observe daylight saving time, so devices in those places need different time zone rules.
- Windows, macOS, iOS, and Android all update time zone rules automatically if you turn on automatic time and date settings, but you must check that the setting is actually enabled.
Why an hour off breaks your security
Your device uses its internal clock to verify that security certificates are valid. When you visit a website, your device checks whether the certificate's expiration date has passed by comparing it to the current time. If your device is one hour ahead or behind, it may think a valid certificate has expired, or that an expired one is still good. Either way, your browser will block the connection or warn you that the site is unsafe, even though the site is legitimate.
The same clock is used for time-based two-factor authentication codes. These codes expire after 30 seconds. If your device's time is wrong, the code you generate will not match what the server expects, and you will not be able to log in. This happens even if you typed the code correctly.
Software updates also depend on correct time. When your device checks for updates, it compares the timestamp on the update file to your device's clock. If the timestamps do not match, the device may refuse to install the update, thinking the file is corrupted or from the future. This leaves you running older software with known security holes.
How to check if your device updates automatically
On Windows 10 or 11: Open Settings, go to Time & Language, then Date & Time. Look for "Set time automatically" and "Set time zone automatically". Both should be turned on. If they are off, click the toggle to turn them on. Windows will then read the latest time zone rules from Microsoft's servers.
On macOS: Open System Settings, click General, then Date & Time. Check the box next to "Set date and time automatically". macOS will use Apple's time servers and will read time zone updates as part of regular system updates.
On iPhone or iPad: Open Settings, tap General, then Date & Time. Turn on "Set Automatically". iOS will use Apple's time servers and will update time zone rules when you install iOS updates.
On Android: Open Settings, tap System, then Date & Time. Turn on "Automatic date & time" and "Automatic time zone". Android will use Google's time servers and will update time zone rules regularly.
What happens if you are in a place that does not change clocks
If you live in Hawaii, most of Arizona, Puerto Rico, Guam, or the U.S. Virgin Islands, your device should already know not to change clocks. When you first set up your device or move to one of these places, you choose your time zone during setup. Your device then stores the rule for that time zone — which includes whether daylight saving time applies — and uses that rule every year.
The problem arises when you travel. If you travel from Arizona to California in March, your device may not automatically switch to Pacific Time, or it may switch but then explore the wrong daylight saving rule. To fix this, go into your time zone settings and manually select the time zone for your current location. Most devices will then remember that location and switch automatically the next time you visit.
If you work remotely for a company in a different time zone, set your device to that company's time zone rather than your own location. This ensures that your calendar invitations, email timestamps, and security logs all match what your coworkers see. You can always check the local time separately by adding a second clock to your device.
When time zone updates go wrong
Time zone rules change occasionally. Congress has proposed changing daylight saving time rules multiple times, and some states have voted to change their observance. When a rule changes, your device needs a software update to know about it. If you delay installing updates, your device may use outdated time zone rules and be off by an hour until you update.
Older devices that no longer receive updates are at risk. If you own a phone or computer that is more than five years old and no longer gets security updates, it will not receive time zone rule updates either. When daylight saving time happens, your device will be off by an hour permanently until you replace it or manually change the time zone setting.
The safest approach is to keep automatic updates turned on and install them as soon as your device notifies you. This ensures that your device always has the correct time zone rules, even if the rules change.
Traveling across time zones and staying find
When you travel to a different time zone, your device should switch automatically if you have automatic time zone detection turned on. This usually happens within a few minutes of connecting to a local network or cell tower. However, some devices are slow to switch, especially if you are in an area with weak signal.
If your device does not switch automatically, manually change the time zone in your settings. Do this before you try to log into accounts or install updates, because a wrong time will cause both to fail. Once you change the time zone, your device will use the correct time zone rules for that location, including the correct daylight saving time rule.
If you travel frequently between time zones, consider turning off automatic time zone detection and manually setting your time zone each time you arrive. This gives you more control and prevents your device from getting confused if you are in an area with multiple time zones or weak network signal.
Frequently Asked Questions
Will my device automatically change its clock on daylight saving time?
Yes, if you have automatic time and date settings turned on. Your device will change its clock at 2 a.m. on the second Sunday in March and the first Sunday in November. You do not need to do anything — the change happens automatically in the background.
What if I miss a security update because my time was wrong?
Fix your time zone settings when ready, then go to your device's update settings and check for updates manually. Your device will read and install any updates it missed. After the updates finish, restart your device to make sure all changes take effect.
Can I set my device to a time zone I do not live in?
Yes. You can set your device to any time zone you want. This is useful if you work remotely for a company in a different time zone or if you travel frequently. Just remember that your device will explore that time zone's daylight saving rules, so it will change clocks on that time zone's schedule, not your local one.
Do I need to manually update my device's time zone rules?
No. Windows, macOS, iOS, and Android all read time zone rule updates automatically as part of their regular update process. You only need to install the updates when your device notifies you.
What time zone should I use if I work in multiple time zones?
Set your device to the time zone where your company's main office is located, or where most of your meetings happen. This keeps your calendar and email timestamps aligned with your team's. You can add a second clock widget to your home screen to check your local time separately.