It used to be 8.30 or 10.30 so the show is after dinner for both main dinner sittings. Occasionally, either on the last night or for certain shows there might be an early show before second sitting dinner but fortunately it's not a regular occurrence.
I agree with @carlmm, I don't want to go to a show pre-dinner. You can't compare cruise ship entertainment to a regular theatre where there is a single performance lasting at least a couple of hours.
Enjoy your last afternoon and evening on board.