JSI Tip 5724. Task Scheduler behavior at Daylight Savings Time transitions and other events.

Microsoft Knowledge Base Article 325413 contains the following summary:

The behavior of the Microsoft Task Scheduler is not specified for tasks that are scheduled to run during the transition hours to and from Daylight Savings Time. Other events can also affect the actual time that a scheduled task runs. This article describes the observed behavior of recent versions of Task Scheduler.