Time Zone Updates on Azure App Service for Windows

2 minute read • By Byron Tardif • October 23, 2026

Update (26 October 2026): The rollout of Windows operating-system time-zone updates on Azure App Service for Windows is complete, following accelerated Safe Deployment Practices (SDP). Application-managed time-zone data still requires separate review as described below.

Time-zone rules change when governments update local timekeeping policies. Apps need current time-zone data to convert UTC timestamps to local time and calculate schedules correctly.

Older time-zone data can apply a clock change that no longer occurs, producing incorrect local-time displays, job schedules, deadlines, and date-based calculations. Apps using different data versions can also disagree about the same timestamp.

What we are doing

We have completed the rollout of an OS-level time-zone update across App Service for Windows through accelerated SDP. This is a platform operating-system update, not a language-specific runtime release.

The platform manages this OS update. Customers do not need to install an OS patch manually on App Service workers. For more information, see OS and runtime patching in Azure App Service.

Windows and application-managed time-zone data

An app can use Windows time-zone rules, runtime-bundled data, or a database supplied by a library. An OS time-zone update alone is not proof that every date/time API or scheduler in your application uses the updated rules.

Review the data source used by your runtime and dependencies. Update application-managed time-zone data separately through the relevant maintainers’ supported update process, then test and redeploy as needed.

What you should do

  1. No manual OS patch installation is needed. App Service manages this platform update.
  2. Check your app’s actual date/time behavior. Test conversions and schedules for the regions your app uses, including timestamps on both sides of the relevant rule change.
  3. Review application-managed time-zone data. Update affected libraries, bundled ICU data, and custom time-zone databases separately. The Windows OS update does not replace data bundled with your app or dependencies.
  4. Update customer-provided container images and bring-your-own runtimes yourself. This platform OS rollout does not patch time-zone data inside your custom image or runtime distribution. Follow the relevant maintainers’ guidance, then rebuild, test, and redeploy.

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