I've not read the monster thread for a couple weeks now. Have we confirmed whether it's "24 hours" or "the day before"? Seems almost everyone had been assuming it was the former, but all the official stuff I've seen from Disney only says "within one day". That can be interpreted more than one way.
(Yes, a day *is* 24 hours, but when we talk about making reservations at 180 days, for example, we just mean which day, and not the time of day.)
In other words, can a Wednesday lunch be cancelled on Tuesday night, or do you need to cancel by lunch time Tuesday?