How Windows manages time zone changes

Brink · Jun 21, 2023

When it comes to keeping the clocks in your organization running normally, you rely on our Windows engineers. We, in turn, look to governments for timely collaboration. Let's talk about the importance and complexity of time zone (TZ) changes, as well as some best practices to help your organization always be on time!

Why are time zones important?
Imagine how difficult it would be for you to coordinate if clocks had shown different times with each passing longitude – a 4-minute difference every few kilometers? That's where time zones come into the picture. They split the earth in near vertical strips and group together places for which it is convenient to have the same time for communication. This helps create a uniform standard time for social, commercial, and legal purposes.

But what if there's a change in a specific time zone? What if a country decides to move from one time zone to another? These and many other scenarios pertaining to daylight saving time (DST) changes create a very tricky situation for countries around the world and for you as an IT pro to manage.

With Windows at the center of computing for a large portion of worldwide devices, it's apparent that such TZ changes must be reflected accurately on devices, on time and consistently, to ensure businesses run smoothly.

The complexity behind the scenes of time zone changes
We closely monitor time zone changes by keeping track of government announcements, updates on Time Zone Database, and when you reach out to our support team.

This sets in motion a series of internal processes that cater to delivering the changes in a period of about 8 weeks. On the one hand, we need appropriate time to ensure the right level of quality of this update, just as we do with any update. On the other hand, we want to avoid unnecessary disruptions for the world by coupling these updates with the predictable update cadence. Therefore, in order to deliver these updates as part of the monthly updates or latest cumulative updates (LCU), the team requires sufficient notice to develop, validate, and release a quality fix. Here's what that timeline would look like!

Illustrative timeline for developing a TZ fix in 8 weeks since government announcement and before DST change takes effect

We can't overlook the fact that sometimes a government announces a TZ change with shorter lead time. The times it has happened, no release vehicle was available that could accommodate a high-quality change in time. Let's learn from a recent example before getting to the practical recommendations.

On August 8th of 2022, a South American nation government announced that a new DST change would begin on September 10th. This one-month notice, unfortunately, was too short to develop a fix with the right quality on time. It was eventually available in the October security update, missing the TZ change trigger date by over a month. Considering an 8-week workflow, we would have needed to receive that notice no later than early July of that year.

But even this 8-week period doesn't account for the fact that the uptake of the released fix often times isn't immediate. Indeed, it is crucial that governments give sufficient time so that we can release TZ changes on time with quality and that users consume them with reasonable planning. How would you do that? Let's see some best practices.

Best practices
For governments
Please help Microsoft provide an update at the earliest and ensure a seamless transition to the new DST and TZ policies. Microsoft recommends that governments provide the following:

Ample advance notice (one year or more, but not fewer than 8 weeks) of the planned change

Official published confirmation of planned changes to DST or time zones

Concentrated efforts to promote the change to affected citizens

If available, notify your Microsoft country officers of the change. In either case, please include this information on the government official website.

For IT admins
Whenever a TZ change is announced by the government, look out for and get the changes built into a specific release.

Keep track of the DST Community Blog. It is regularly updated to announce when Microsoft becomes aware of a TZ change, when it will release the fix, and if there is an interim guidance to be followed.

When changes are delivered via a preview release, download and install it as soon as it becomes available for your devices. Preview releases often provide an early opportunity to test and implement the time zone fix.

How to get the time fix
When a time zone change is ready to be shipped, get it for your organization through a specific release via Windows Update.

You can get the change as part of the monthly security update, released on the second Tuesday of the month. As such, it reaches all the supported devices through your regular update management process and without any intervention from your end users.

Sometimes the change is part of the monthly optional non-security update, released the fourth week of the month. You'd need to download this update from Windows Update to get the changes. If you don't install it at this time, the change is automatically included in the next monthly security update.

Read about the difference between these releases in Windows monthly updates explained.

Check out Daylight saving time help and support for details about our notice time requirements, our support policy, and solutions offered for different time zone scenarios.