I don't know, I called Disney on June 21 for an overnight on June 22. It must be easy like that all the time. (end tongue in cheek comments)
The above input is good. We're booking a Disney trip for February and my has had her 180 day calculator set to tell her when she can start making advanced reservations. She wants to do the "Be Our Guest" dinner at the new part of Magic Kingdom.
If you can and are willing to deal with taking the kids out of school- the more you can target the off-season, the better your experience will be.
Well, maybe not "better"- just "different in a good way". That said, we did Christmas in 2012 and the wife loved it. I don't think I could do it again, but I'm sure she would gladly go back.