As the rule was explained to me, its 1 bump in each new 24 hour period (so if you wanted to bump at 23:59 and then again at 1:01 that would be in different 24 hour periods). I remember Racer being clear about this. However the first post in a for sale thread is not a bump, so if you do wish to bump it within the first 24 hour window of posting the thread that was OK as well, but no reason to do that really.