Disney will be happy to take your AP $ at any time. ;-)
How familiar are you with AP room discounts? I'd suggest posting on the Resorts/Discounts board, you'll get plenty of feedback.
But FYI, you don't have to have an AP purchased to book a resort room with an AP discount. You just have to have it when you check in. It doesn't make much sense to buy one now for something that far away (you're just letting Disney have a lot of your money today with no benefit to you).
Also just in case you don't know, AP room discounts act like all other resort discounts... availability can be limited and varies by resort, room type, time of year/promotion, etc. Just because you have an AP doesn't automatically mean you get a room discount. (Sorry if you already know this).
Hope that helps!