I booked a bounce back trip when we were there in December. The dates were on the computer (CR has in room computers) under my messages. If you don't have a computer just ask at the front desk or use the phone in your room to call reservations (I don't recall the onsite phone number). As posted in December, the 2008 bounceback dates were:
1/6 to 2/2/08
2/24 to 3/1/08
3/30 to 4/12/08
8/10 to 9/27/08
These dates apply to deluxe reservations. (Villa dates are roughly the same but the offer for them is 40% off.) The Moderates may also be included (but they were not listed on the computer.)
The instructions say you must book before you checkout (I'd be interested to know if there is some flexibility in this requirement).
I originally booked an April bounce back but when I returned home, I changed the dates (to January) and still received the 30% discount. I've heard there are other bounceback discounts such as the dining plan but I didn't see those listed at the time.
Also, it took about 20 minutes to get through to the reservations personnel from the hotel room phone when I called so be prepared to leave plenty of time when you call.