If your start time is in A2, duration in B2, night shift start time in C$2, night shift finish time in D$2:
Finish time would be =A2+B2+IF(A2+B2C$2,MOD(D$2-C$2,1))
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David Biddulph

"Martin B" wrote in message ...
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