A friend of mine works in a pizza parlor here. In a meeting with the owner yesterday, he was told that if they ended up staying late b/c customers came in close to closing and were still eating he didn't have to pay them past the hours they were scheduled , that it was there problem that they stayed late. But he doesn't allow them to tell people they have to leave. He requires them to keep the kitchen open til closing i believe.
Can he really get away with not paying them if they have to stay late?

No, He's full of it. Employees need to be paid for all hours worked. He's setting himself up for a nice unpaid wage claim.

How much time per week are we talking about, roughly?

I assume these are non-exempt employees - if so, they have to be paid for all hours/time actually worked.

what do you mean by non exempt?

All employees are assumed to be non-exempt unless they meet the criteria for one of the classifications of exemptions AND the employer chooses to treat them as such.

http://www.dol.gov/esa/regs/compliance/whd/fairpay/fs17a_overview.pdf

Non-exempt employees get paid OT, exempt employees get paid a regular/fixed weekly salary no matter how many hrs. they work.