A subtle thing that restaurants do is say: "We are doing last call, would you like to get a drink?"
The practically of this question, is that in a lot of ways it shouldn't entirely matter. Yes, I may have lost track of time but did you really need to remind me?
The real value of the question lies in a thought experiment: If I wanted to increase drink sales and I only had two options 1) Stay open 30 mins later in the night or 2) Close 30 mins early and say the last call line - would I have more sales in the latter situation because there is a time constraint?
I don't know. What I do know is that there are always these last call lines in any type of businesses we work in. What we learn about them, is little questions, asked at the right time, have the potential to make a big difference.