I know my BO extremely well and am also an assistant trainer at my farm. BO lives on the property full-time as well. We don't have "barn hours", so to speak. During the week I am forced to come up later in the evening. I don't typically get there until 8 and sometimes even 9. I am courteous about what I do though as I feel terrible keeping the horses up late.
At a busier facility, I would imagine that being open until 9 PM is fair. I understand it is likely a huge liability to have people there late when there isn't as much foot traffic in case something happened. There's also the irresponsibly night-goer who forgets to latch gates or shut lights off..