MicrosoftWe've noticed an issue with our Windows-based Teams Rooms appliances, where the Teams Rooms interface displays the clock and meeting times one hour behind the actual BC time.
The issue appeared after our W11 IoT devices received the update and switched to the new BC time zone (UTC-07:00). We've confirmed that Windows itself displays the correct time and UTC-07:00 offset. However, the Teams Rooms application displays both the clock and scheduled meeting start/end times one hour behind (UTC-08:00).
Our Exchange Online resource mailboxes were originally configured with Pacific Standard Time. However, updating them to BC Standard Time, Yukon or US Mountain Standard Time (Arizona) did NOT resolve the issue, and the only workaround is to change the Windows time zone to Arizona or stay with Pacific Time (US & Canada).
Get-TimeZone shows the new BC Time to have BaseUtcOffset -08:00:00 and SupportsDaylightSavingTime set to True. I think this is for backward compat, but not working well with Teams.
Is there a minimum Microsoft Teams Rooms application version required to support the new BC time zone, or is there a known compatibility issue beyond the Windows/Exchange Online time zone configuration? Do we need to be on Arizona or Yukon time?
Edge, Chrome, Firefox, Teams Desktop, and likely many other applications show an time that is off by one hour. I have done a bunch of troubleshooting on this, and traced it down to ICU library issues (as mentioned earlier by GGrisAct3D). I have also come up with a fix.
Windows bundles ICU (International Components for Unicode) libraries. These libraries are used by many applications, including the ones listed above. Additionally, some applications bundle their own copies of ICU libraries.
One of things this library does is provide a mapping between windows time zones definitions and the IANA tzdb names (like "America/Vancouver"). In order to work properly, these mappings need to be updated to include the newly created time zones. The latest windows update does not include the updated mappings, nor does the latest tzdata "icunew" release from ICU (version 2026e).
It's possible to address this as follows:
This causes any applications using ICU to load the updated/custom definitions. Placing it under system32 is necessary to work with Firefox, otherwise Firefox's sandboxing will block access to the .res files. This fix may not work for UWP applications, applications that bundle ICU with compile time settings to disable external resource loading, or applications that bundle very old versions of ICU. I have tested it with Edge, Chrome, Firefox, and Teams Desktop - it worked for all of those.
