Personally, if either of the rebates require you to cut anything from the MBP box, I'd wait until after the initial 14 day return period.....just in case the system has a flaw, you can just return it, in the box and get a new one.
I did this with my MB.....I got in on the printer deal and it required me to cut the UPC on the MB box. Well, 2nd day, noticed my arrow key wasn't working correctly.....no way I'm keeping a machine, or getting it repaired in the first 14 days. So I took it in, all in the box, they exchanged it on the spot. I'd have to imagine that if I cut the box, then I'd be stick with the machine and getting it repaired.
I'd say, wait until the day after your return date on the receipt....then submit away!
-Kevin