A couple weeks ago, I booked for two days, one on June 7 and one on June 10. I had a resort reservation that covered both of the days, and they allowed me to book both days on the first day that June 7 was available (60 days out).
I waited about 15 minutes, so I was happy I didn't have to call again for the June 10th one.
Note that both of my days are my Hollywood Studios days, and the CM suggested that I don't try to get Ride of the resistance during the tour (mainly because of the length). Those are my only two days though and I already had all my dining reservations plans done, so it would be too hard to move around.