Mandalay Bay is brighter and is supposed to have a younger crowd than most casinos. Most casinos are dark and there are no windows, so it really doesn't matter what time it is.

I've "gotten up" to play blacjack in the wee hours of the morning at several casinos, and you tend to have the real hardcores at the table, which makes it interesting. However, I would not describe it as rowdy.