The words matter, so I'm to answer the question by addressing an actual Move, "Make Camp".
The players declare they are going to "settle in to rest" (Make Camp's trigger). There is no roll. Thus you decide whether or not they will succeed.
Essentially, you make a move. Quite often the appropriate response to this is the Opportunity (with no cost) for that rest to succeed, and thus some sensible amount of time passes; enough time to sleep, Commune, Level Up. However long the players want.
Other times, you'll have good reason not to let make camp succeed. If there's a monster stalking the party that they don't know about, you'll Reveal the Unwelcome Truth that they aren't safe, and they'll rest just until the monster arrives; not long enough for anything. If they're in an adventure, you can make an adventure move; they settle in long enough to be disturbed the the cavern's periodic Flooding. Or advance a Grim Portent; they're settling in, but hear the screams of the Goblin that's being sacrificed by the vestal maidens.
How long this takes is then purely driven by the fiction. If they sleep the night, then that's how long it is until morning, or whatever the players say. If something that you do interrupts them, then you say.