Depending on where you want to stay, it might not be difficult at all. Last year we were able to book a week in early November (F&W, Jersey Week, & SuperSoap Weekend) at 5 months out. I had to waitlist for the resort I wanted, but that came through at about 4 months.
However, just to be on the safe side, I'd book at my home resort at 11 months and then try to switch over at 7. At least this way you'll have a place to stay.