I work for a medium size charter company that has approximately 30 pilots. We have an Astra, 2 Hawkers, a Falcon 50, 3 Citations, 3 King Airs, and around 12 Caravans on our certificate. Our full time pilots are on call from 4am Monday morning through 4pm Friday night. Weekends are optional, but you are encouraged to make yourself available every once in a while should something pop up. We have a board that shows when we have trips scheduled for the next month or so, but a crew is not assigned until the day before. If you look at the board, you can get an idea of when you might fly, but you won't know for sure until you are dispatched the day before. I'm checked out in the King Air and Caravan, and so far i've been averaging anywhere from 2-4 overnights per month. In another week or two i'll be checked out in the Citation as well, which will probably mean an extra couple overnights. Generally speaking, the bigger the plane, the more overnights you will have. The Hawker pilots often spend several days away from home at a time.
Like cvsfly said, you are likely to get many different answers. Some companies do operate on set schedules with "hard" days off, but those are usualy the larger companies. Anyway, hope this helps and was what you were looking for.