[quote name='eau']limit of 5 rebates per person per month. Is it based on the postmark date or what? That is, I could mail 5 rebates in one envelope on 2/28, and then another 5 rebates on 3/1 and still meet their requirements, right?[/QUOTE]
Yes, as long as the due dates on the rebate forms are the end of the month in which you get the postmark (thus you could send in 5 rebates due Feb 28th or later on 2/28, and another 5 due Mar 31st or later on 3/1).
Probably, though, to avoid hassle, I would send them a little further apart, and not tempt fate with the very last day in Feb. While you can always get it sorted out, they might initially disqualify some of them as being over the limit.