The amount you ride in a 12 or 24 hour depends on your training and goals for the race. I train to ride the whole time as my goals (set at least 4 months before the event) are usually to be in the top 1/3 of women.
I don't stop for anything other than a refill of the camelbak ( I use all liquid nutrition) or when nature calls, and the goal for my stops is to keep them to less than 2 minutes.
However for as many of us wing nuts out there burning up the miles there are still plenty who do a few laps, rest, cheer on other riders, have a snack, and then do a few more. It is all about what you want out of the race/event.
Having fun is the most important thing! If you aren't having fun why would you do it?