it's already in

OA -> Battle Simulator / Fleet Scheduler : in Battle Simulator select needed fleet configuration, define source&target planet, speed, mission, then define Execution time [hour:mins:sec], click on 'Add ->' button, done
P.S Much better if you have an OA server account, you define your scheduled fleets and in Bot/Hunter right click on targets -> 'Send the Attack' (this way it's added in scheduled fleets list). Then you shutdown you computer and you go to sleep, OA server will continue to do everything that were defined.
