for some reason you might want to rerun an application very day or every hour. In commercial applications, one may want to let the device sync data every 4 hours, So you need an application that runs periodically at specified times or intervals. As this first sounds easy, it is not as simple as you mean.You cannot simply use timers, timers will not continue to run within Suspend mode.
To have an application run at specific times, Windows Mobile supports a notification database. Your device will already wake up periodically to reschedule events and to clean up the notification database. Normally, Windows Mobile Phone devices will awake every night at 0:00.
There are also some other possible notifications that can launch an application, see my old web site.
How can we do a scheduled application ourself? At first run, the scheduler application has to delete all previous notification entries of the notification database. Then it has to create a new timed notification and in our sample, it will then launch another application. The scheduler application itself should be small and only care about the schedules. The worker application can be what you want and will be started by the scheduler application.