The offer clearly states you must still be on property to book- no exceptions (I think this means it must be before 11 pm on your checkout day). Both times I have booked a bounceback they made sure I was still on property.
I called once at 10:30 pm on checkout day and was told that no one who could book that offer was available. Called back the next day and was told could not book. I play it safe now and book well before checkout.
I agree that the bounceback for 2016 is not a great deal. Our package for 2016, with a moderate standard room and FD was $500 more than the same package for 2015.
It could, however, be the best deal available by next summer, so I booked thinking I might cancel if I can get a room only that doesn't require the park hoppers or water park tics. Given how things have been going, discounts are getting worse and harder to come by now. I didn't want to be stuck on hold trying frantically to book a discount when FD is released next year.