I need to make an appointment for one of my daughters. I keep forgetting to call, and finally remembered late Friday afternoon. I called at 4:01, glad that I'd remembered, since I figured they closed at 5pm. I got the after hours recording. So I assume they must have closed at 4. If I'd called 5 minutes earlier, I might have caught somebody on her way out the door, and never even known that they were closing 5 minutes later, as 4pm seems awfully early to close up shop to me. So it can definitely happen out of ignorance of the hours.
I used to work in a library. Many of the jobs required a master's degree, so we're not talking about a part-time minimum wage job. The library would close at 9, and that meant that at 9pm, all customers were expected to be walking towards the door. There were many warnings as the time got close. It would sometimes be a few minutes after 9pm before we could lock the door behind them. Then we had to do various closing activities, gather our things, and wait for the person in charge to finish specific closing out procedures on the registers and such. It was never before 9:15 that we left, even with the very fastest closing manager we had. When we had abandoned children or an incident or some-such, a manager and a second in command or the security officer often had to stay until after 9:30, maybe 10.
So no, I don't consider it unusual to be expected to keep working right up until your "done" time, and then take a few more minutes to finish things up. When my boyfriend worked at a pizza place, as long as you walked in the door before they were closed, they'd serve you. When I worked in a physics lab, I kept actively *working* right up until 5pm, and then had to do various closing-up activities before I could leave. I think it's just the way the world works, generally.