There is a RAW answer for how much time camping normally takes. In the forced march section of the overland movement category in the SRD, it states:
In a day of normal walking, a character walks for 8 hours. The rest of the daylight time is spent making and breaking camp, resting, and eating.
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 elves 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 some 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 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 spellcasters that is kind of vague. For wizards (and other arcane spellcasters) though, it is very explicit:
To prepare her daily spells, a wizard must first sleep for 8 hours. The wizard does not have to slumber for every minute of the time, but she must refrain from movement, combat, spellcasting, skill use, conversation, or any other fairly demanding physical or mental task during the rest period. If her rest is interrupted, each interruption adds 1 hour to the total amount of time she has to rest in order to clear her mind, and she must have at least 1 hour of uninterrupted rest immediately prior to preparing her spells. If the character does not need to sleep for some reason, she still must have 8 hours of restful calm before preparing any spells.
The prepared spellcasters (wizard, cleric, druid, etc.) have the worst lot for spell prep time:
Spell Preparation Time
After resting, a wizard must study her spellbook to prepare any spells that day. If she wants to prepare all her spells, the process takes 1 hour. Preparing some smaller portion of her daily capacity takes a proportionally smaller amount of time, but always at least 15 minutes, the minimum time required to achieve the proper mental state.
While the spontaneous casters get off fairly easier:
Daily Readying of Spells
Each day, sorcerers and bards must focus their minds on the task of casting their spells. A sorcerer or bard needs 8 hours of rest (just like a wizard), after which he spends 15 minutes concentrating. (A bard must sing, recite, or play an instrument of some kind while concentrating.) During this period, the sorcerer or bard readies his mind to cast his daily allotment of spells. Without such a period to refresh himself, the character does not regain the spell slots he used up the day before.
Divine spellcasters also have a fun quirk that adds to that:
Time of Day
A divine spellcaster chooses and prepares spells ahead of time, just as a wizard does. However, a divine spellcaster does not require a period of rest to prepare spells. Instead, the character chooses a particular part of the day to pray and receive spells. The time is usually associated with some daily event. If some event prevents a character from praying at the proper time, he must do so as soon as possible. If the character does not stop to pray for spells at the first opportunity, he must wait until the next day to prepare spells.
What does everyone else do while the spellcasters clear their minds?
Those dirty plebeians are probably the folks responsible for the bulk of 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.
For some additional detail (there are lots of lovely buried details), I would recommend reading the overland movement and relevant selections of the magic overview from the SRD.