I had certificates that were supposed to expire on 12/1. I had them tied to a November reservation, but I wanted to book something in December that would have been a better value. So I called the diamond desk, didnt ask for any details, and said would 1/1 be a helpful extension date. I said yes, he moved it, and then I booked the new reservations. I didnt even need it extended that long, but he said with travel always changing around the holidays he would give me extra time just in case