It could be quite a wait! We are flying to WDW the last week in April. All of our resort package was booked, but SW was only accepting reservations through April 4th. Just before Christmas they finally extended it to June. My advice, check the site daily (multiple times as we did) the day it opened up we had checked in the morning before leaving for work, when we got home discovered it had opened sometime in the middle of the day! We got 9 of the last 12 seats in the time frame we were looking for.
Good luck and have a great time.