It's 9am and 2:30pm, but they won't necessarily have both (or even one) tours. It depends on how busy they expect the park to be that day. I had planned to do the tour on Tuesday when I went, but there were no tours that day and I ended up with Sunday afternoon.
If you have AAA you can get the tour for $39. I think it's definitely worth it. You get to go in Club 33 (the lobby)!