So, the whole sleep/camp experience is taking the other 16 hours of the day.
How much of that is actual rest/sleep and how much is other stuff?
Well, that depends on your party. If you have a party of Elveselves that doesn't include arcane spellcasters and nobody keeps watch, they trance for 6 hours and they're done. If you have a party with mostlysome non-elves or some arcane casters and you set watches, it can take much longer. With 4-hour watches, the rest period takes 12 hours (and requires 3 watches), if you set 2-hour watches, the rest period takes 10 hours and(and requires 5 watches). That assumes that everyone needs 8 hours of rest.
So how much of that rest is sleep?
Again, this will depend on your party. For elves and warforged, the answer is none, ish. For other races that aren't wizardsspellcasters that is kind of vague. For wizards (and other arcane spellcasters) though, it is very explicit:
The prepared spell castersspellcasters (wizard, cleric, druid, etc.) have the worst lot for spell prep time:
Divine spell castersspellcasters also have a fun quirk that adds to that:
What does everyone else do while the spell castersspellcasters clear their minds?
Those dirty plebeians are probably the folks responsible for the bulk for the camp chores (gathering firewood, cooking, setting/packing up tents, etc.). They might also use the time to bathe or do other grooming (that monk does need a polished hairless head after all!). You might also let them indulge in some craft time, albeit at the hourly rate (progress measured in CP). If you really want the characters to feel lived in, maybe ask the players who get what chores, how they feel about them, and what they do in their other time. I would recommend only getting into that level if detail if they're interested in it though.