If at first you don't suceed, try, try again!
I started trying 90 days from our day of arrival at the world at 6:55 a.m. and they were all booked. I tried every morning for the next 11 days with no luck. After that I tried about once or twice a week with no success until SEVEN DAYS before we left and there was a cancellation for the night that worked perfectly into our plans! I kept it a secret from my family and made it my surprise for the kids and the other family we were going with. It was absolutely awesome, but I thought I was going to burst keeping it to myself!
Good Luck!