When does the game save in single-player?

[Vanir]

Does it save when you sleep? Or when you quit? If so does it keep your current position, or spawn at the base?

[Monokuma]

You keep your current position. I know it saves when you quit, but I believe it also autosaves periodically as well.

[MechWarden]

It auto saves every 5 mins, and I think that's mostly it...?
(honestly, for playing over a hundred hours, I'm actually at a bit of a loss here)

It does save where you were at, so you can quit (and save) practically anywhere and return later almost like nothing happened. Though some things like loose items on the ground do get cleaned up; except for lost loose items, which will magically pop back up on the ground after a reload.

I always "Force Save" via the Admin menu (via the Esc/Pause menu) before quitting just to make sure. I had some cases where I lost a few minutes, because it didn't quite save when quitting, which honestly isn't that bad.