No, I wouldn't be mad. Maybe a little relieved at having been given a "grace period" before I have to pay for it. In any case, I would treat it as money already spent (i.e. deducting it from the check register) as I don't expect to get it for free just because they are slow to charge my debit card, nor do I want to accidentally spend the money again. I don't know what the rule is for a time frame, but as long as you deduct it from your check register right when you made the purchase, it shouldn't cause you any problems in the future.