I have a spread sheet used for production planning which predicts the finsh time of a job depending on its duration. This works fine but I now have the problem that production is no longer 24 hours so if a 12 hour job starts at 15:00, no work will be done between 21:00 and 06:00 (9 hours) so it will finish at 12:00 noon on the following day.
Is there a formula that will add 9 hours to the duration if the calculated finish time falls during the night shift?

Thanks in anticipation
Martin