An agent I spoke to last week says that the 24-hour cancellation policy is, in reality, a "by-the-end-of-the-next-day cancellation policy" because the reservations don't have time stamps, only date stamps.
Theoretically, you could make a res at 12:01AM on 12/24 and cancel is at 11:59PM on 12/25 -- and get a two-day "hold".
Can anyone confirm?