There's plenty of threads about it on here. What exactly do you need to know? I flew unscheduled 135 for over a year and a half(2000hrs), so hopefully I can help you out a little.

Pilots must have 10hrs of rest within the previous 24hrs, so essentially the "duty" day is 14hrs

Also there's the 8hrs of flight in a 24hr period. I always interpreted this as a rolling 24hrs to cover my rear.

Now, the kicker is you do a live leg of say 6hrs, and you're 4-6hrs from home, you can elect to fly home at that time, because it's Part 91. The next day at the end of your rest you get a 3hr trip, can you fly it?