Interim guidance for British Columbia time zone changes 2026

I believe this might be related to this issue we had on the next windows update:

Affected version: Windows preview update KB5124010 (OS build 26300.9550)

Description:

On systems configured to use the new British Columbia or Alberta time zones, the Windows ICU API ucal_getDefaultTimeZone() returns Etc/Unknown with a success status (0), instead of a valid time-zone identifier.

Reproduction results:

British Columbia Standard Time → Etc/Unknown (status 0)

Alberta Standard Time → Etc/Unknown (status 0)

Yukon Standard Time → America/Whitehorse (status 0)

The issue reproduces outside our application on the affected Windows build.

Impact:

Applications relying on ICU to determine the system time zone may fail when the returned identifier cannot be resolved. In our application, before we patched it, this caused an uncaught std::runtime_error during startup and terminates the process.