What I've seen is a couple different models. There are some companions who offer overnights that're only up to 8 hours and yes, some of them are willing to pull an all-nighter. And then there are companions who have an extended 12-16 hour overnight package where uninterrupted sleep is required.
Sleep deprivation is a form of torture. I'm not sure why y'all don't understand that a well-rested provider can do more for you.. Either way, no, do not assume that someone wants to skip out on sleep and have their mind and body feeling wrecked for the next day or two. Simply ask the person you're thinking of booking how they structure it.
Lastly, there are some companions who offer an extended 12 hour / clock-free daytime date for the same rate as an overnight.
Not only is MSOG expected on overnight visits, very little if any sleeping and all night fucking is also expected.