Be careful planning to cancel on your day of check in. MS says 48 hours. Once the resort has your reservation, MS may have to cancel and rebook that reservation without the ddp. That could mess up your points and could take much longer to checkin.
Something similar happened to me at SSR when we upgraded from 2 studios to a 2 bed at check in. I was happy they could upgrade us, but the ddp and cancellation of studios was a total pain. I had guests, and it took a long time and my points were mixed up.
I believe they say 48 hours because MS still has control of the reservation. On the day of check in, if you check your online account you will notice your reservation has moved to the "completed" list. Once completed, all bets are off. Also why cancellations on the day of check in result in a forfeiture of points.