We arrived at 9.30 am on a Monday. So we missed the initial entrance time. (Misled by our gps...) However, I can tell you that at 9.30, every single bus time to the Saturn center was available.
Also, at approx 1 pm, the IMAX theatre still had seating available for that show.
We would have had no problem using our AAA tickets throughout the day. Of course, your mileage may vary.