For a trip beginning May 14, 2015, you'll be able to book other DVC resorts beginning October 14, 2014.
Availability is dependent on several variables, but mid-May usually has good availability at the 7-month window. The key to finding availability is to remain flexible. If your first choice in resorts isn't available, then be prepared with a second or possibly a third choice. Sometimes, we'll tweak our dates if our first choice is already booked.
Now that you are a DVC member, you can sign on to the Member website and use the new Resort Availability Tool to see what is still available as you get closer to your 7-month window. The Tool is under the "Vacation Planning" tab. You enter your dates and the resorts you want to check. The Resort Availability Tool will show you, by Accommodation Type, what can still be booked.
Good luck!