You can use AlarmManager to make Android call your app at a specific time. You can do this pretty simple like this:
AlarmManager.set( AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() +
TWENTY_SECONDS, yourPendingIntent )
Then you should register a BroadcastReceiver which will allow Android to send that intent to your application at specified time.