Originally Posted by fassy

Depends on the T&C of the lounge, e.g. most of the Priority Pass or independent contracted lounges allow a maximum stay of 3 hours.

For the Gold/Business lounges of airlines you are mostly restricted by their opening hours. A lot of them are not open for 24 hours. Anyhow, if they are it shouldn't be a problem to stay as long as you want if you got in. (most lounges will only let you in with a same day boarding pass)

Anyhow, maximum stay length is hard to enforce once you're in.