You shouldn't have any problem. And if the exact time you want isn't available when you're booking, there's a good chance you can get what you want onboard. We had a situation where we had DD booked for a pirate makeover and then a few weeks from sailing, they changed pirate night on our cruise and moved our BBB booking to a different day. Well, we had an excursion that conflicted and there were no other appointments on the new day that would work. Once on board, I went to guest services and they were able to get me the exact time I wanted. They had plenty of times held aside for booking on the ship.