I did this last year, start calling about 5 minutes till 6 am Florida time and be on a phone that has speed dial. If it is busy, hit flash and redial until you get a ring. As soon as you hear a real voice have the date and time you want ready so they can type it in. Say, Cinderella's Royal Table, Dec. 6th ,8 am. If it takes more than 3 minutes to get through from the top of the hour you probably won't have a chance but Grab whatever they offer because if you ask for a different time than the one they offer the original offer is given to someone else. If you get to 8 am seating you can be finished with your meal at 9 am and out to Fantasyland and onto the rides with no waiting. We rode Snow White, It's a Small World, Winnie the Pooh and Peter Pan several times with no wait and then went over to ride Buzz a few times. That was what was so great about the 8 am time. I think there is a forum about this somewhere here.
I think they require a credit card now so have that ready, too.
Well, hope this helps. Have a fun trip!!!