I get the point, but I assume the people keeping the museum open at 2 AM for some rich dude are the same people who do exactly that kind of job in normal hours.

In other words, they are asked to do overtime. So, as long as they are getting adequately paid for that overtime and they are not forced to do so (but I assume you can always find at least two people out of 20 who could do that), I don't think it's a big deal.