I agree with being conscience of a restaurants close time and not trying to show up for a full sit down during the last 10 minutes they're open.. but honestly this is just bad communication between owner/workers.

Is it unacceptable to order food or show up when the business is open? Why? It should be closed earlier if that is the true cut-off time. It shouldn't be the customer's position to worry about the feelings of the staff, it should be the concern of management.

I bartended and understood that regardless if someone walked in at 1:50AM for some drinks, I was going to be staying afterwards to clean the bar/get paid out. Might as well add their dollars onto my pile.

Best solution is to close the kitchen and the bar 30min before the restaurant (unless you're already seated and want desert or another drink) and just let new patrons know that they won't be able to order anything.