I would think like a lot of places, by the time your asked to leave, you're about ready for your morning cup anyway. Which, suprise, suprise, the Walmarts around here usually have a McDonalds. Sorry Mr. Manager, I was just waiting for McDs to open. I'll be gone as soon as I grab that $1 large. A Walmart is usually just an emergency overnight stop since you cannot find something better. And I suspect, like most night shifts around the world, their give a **** meter will be pegged long before they see you in the parking lot and they won't bother with you until morning. Just be polite and apologetic if you are asked to leave. Chances are, if your polite, they'll tell you its ok "just this once."