Well, I'm not going to tell you to wait, BUT in the past the availability has generally been a lot better than what the people on this board would make it out to be (no offense to the 'i have to call at 7 am on the day it's released' crowd), especially if you are not really set on what resort you want.
Does the booking window even extend to mid-july? In the past I have booked at the end of june just before the offer ended, and that was after the end date was extended. I didn't have any trouble getting the resort I wanted (All-Star Music) for Sept., but it may have been tougher to get if it was in mid-august.
Why not just book now and just not worry about it? you'll be able to fully cancel until about the beginning of july.