We are leaving for a trip on July 1. Our 7 month window for changing the resort begins on December 1. It is my understanding that I can book 7 night at that point. Since I need 12 nights, I guess I have to call day-by-day to add that extra room. This day-by-day thing worries me, as I guess it is possible that I will get some days and not others. Any tips for tilting the odds in my favor? Part of me was thinking that perhaps I should just book the first 7 days and then wait until 5 days later to call for the remainder of the days. Even though my odds might be lower, it will be less of a hassle and I can simply move to another resort with vacancy if nothing is available in my chosen resort.