Well, I guess the post number could be exchanged with a date and the check is made against todays date instead of the post number. The problem is that this is only run in addpost.php, so it wouldn't update until they write a post. Don't know where a better place for it would be though, maybe the login page, at least something that's not run very often since you don't want to have to do lots of extra file accesses and stuff.
