If you are talking about the one bedroom DVC villas, you need to book immediately at the 7 month mark. If you can't get all your days, setting up a waitlist may work out. It seems like people book there if they think there is any chance they may stay there and then cancel later if they realize they won't be staying there. Remember, there aren't many rooms there to begin with (48 total of all sizes, I think) and there are thousands of DVC members.
If you are talking about the one bedroom suites that you book through the hotel, I think 7 months is plenty of time. I've looked at the one, two and 3 bedroom suites during the summer and usually see some available at 6 months out and even less sometimes.