The main shows are performed twice so each seating can attend. The show for those with late seating is done before dinner time. Those with early seating have their show after dinner. Of course you can go to either show if you want to skip the dining room and eat at the Windjammer, or if you have reservations in one of the upscale restaurants.
There are also some days when only one show is done, and in that case it is usually done late - 10pm or so. But these are not the production shows with all the dancing and singing.