Norm - Did this person at the MGM desk have a big smile on their face when telling you this story ?
It is not true in any way shape or form, the computer board it the slot can't be programed to pay more or less during the first 24 or so hours, and if it could it would be in violation of the gaming commision rules.
Anybody who has taken apart or seen the working of the slot machine would know this can't happen, your person was more than likely doing their best to get people to the MGM to plat, the more play the better chance of a payout but not always.
Walt