Once you establish this policy....all you will do is chase out customers to local coffee shops and Starbucks. If I were Burger King....I’d seize on this and have an ad (’We don’t chase out customers’).
I have seen it done during overnight hours to keep the drunks and teens away. One place had something like a $2.00 per hour minimum. Just google Denny’s Fights and see why some places have this policy.