We tried to do NASA on our disembarkment day. The tour itself takes about 2 1/2 hours, which was about all we had. We only had time for one of the other exhibits, since our flight was at 3:00. Then we rushed to the airport only to find out our flight was delayed!
It probably takes about 4-5 hours to do everything at NASA. Also, you are definately no longer in WDW - the lines for things move very slowly.
Lisa