We were there last Wednesday. Bought tickets there. The are no assigned times. Be sure and allow plenty of time. We bought the combo ticket to go to the aquarium also. We spent around 5 hours going through with about 30 min. break for lunch.
Once there you can ask for a change of time, which was what we did when we were there!
Times are only required for,guided tours etc and for,them to estimate the amount of people in the building
There are no assigned times you just have to be there in between the open to close hours
Thanks! Your answer is awaiting moderation.