You have the day of checkout 10 pm to book a bounceback. I decided to do it once we got home and I called 9:45 pm, was on hold for 10 min. and squeezed in. Apparently they tie your reservation number to the offer, because by the time 10 pm had passed my info was no longer in the computer and they had to fish for it. I was lucky I called when I did; I thought it was a 24 hr line and it wasn't, they told me they start closing the lines down 9:50.
I guessed the week that school will have their fall break for next year but the CM assured me that the main point was to book it to tie the offer down. Changing dates or resorts at that point is no big deal. She was great to emphasize the dates for cancellation without penalty, and when ADR's would start.