On starships they have artificial light in different sections that are synchronized to duodenal cycles to assure continuous coverage and crew morale (except deck officers who never sleep unless they are to be mentally invaded).
The pre-letter Enterprise didn’t even have holo-decks so the submariners should have done this long ago.
You have to do SOMETHING to break the monotony.
Bug juice instead of coffee...something. Omelet instead of over easy...
You must have meant “diurnal” cycles, I bet. “Duodenal” would refer to a segment of intestine.
When do the girls sleep? Where do the girls sleep? What a joke.