Oh that's one thing I didn't think of.
Their discounts work in two ways: with one type, the discount will simply apply to whichever dates of yours are valid under the discount. If that's the case, and all of your original dates were valid discounted dates, then you have no problem.
Other discounts (like free dining) are based solely by check-in day. You have to check in during a valid range of dates, and the discount extends to your entire stay. If that's the case, you will still need to make sure your check in date was during a valid arrival date.
Hopefully that makes sense. Without having the specific bounce back discount in front of me, it's hard to say. However, bouncebacks seem to be much broader and flexible, with a wider range of dates, so there's a good chance you'll be ok.
Edit: I forgot it is room only, so it should certainly fall into the first category. Only certain package discounts would have the restriction of needing to check in by a certain date. Room only discounts will simply apply to whichever of your nights were valid under the discount.