This takes one conversation. “Closing time is 9:30. That’s when you turn off the sign, close the doors, and stop
admitting new customers.”
“You’re being paid to work till 10:00. So you welcome new customers into my Chic-fil-a all the way up to 9:30. Serve them with a smile and clean up afterward.”
“If I find that you’re not following my policy, you’re fired.”
To give my employees cover, I’d even put a sign on the door that tells customers that by company policy, I don’t allow my employees to admit customers after closing time. But also has a phone number for them to call if they find the store closed at 9:29.
Adjust those time periods as needed for your specific establishment.
Ta dah!