This property is not supported for ScheduledTask objects in the current version.
Assembly: Microsoft.Phone (in Microsoft.Phone.dll)
ScheduledAction, the base class for ScheduledTask, exposes the property, indicating the time at which the schedule starts. In the current version of Windows Phone, scheduled tasks cannot specify a begin time. The execution schedule for these objects begins as soon as they are added. Attempting to set this property will throw an exception. For more information about using scheduled actions, see Background agents for Windows Phone 8.