Ahhhh, good question. This is one of those new improvements. Of course LEGALITY speaking the company only has to give you the FAR minimum. But as far as company guideline (and common sense) addressing fatigue issues inherent with on demand flying we use risk system of a sort that tells SOC how tired you are. If you need more rest than 10 hours you let SOC know at the end of the day prior, if you have been getting beaten up they are probably looking at if there's a way to ease off on you (sometimes there is not short of calling fatigued). There's the occasional "you said you wanted 15 hours but we can only give you 13 hours tonight but I've shortened your day tommorrow. Type scenario". The bugs are still being worked out but it's definitely a step toward a generative safety culture.
An example where logic and sense prevail over legality:
0600 duty on in TEB for 0700 wheels up
Arrive VNY at 1000 and duty off at 1100 and go to the hotel. Say both live on the west coast and probably won't be thinking about bed until 2200ish. Considering only the minimum rest requirements they are legal for a redeye even though they haven't slept since 0200PST that morning. If you don't actually think about what you are going to be doing in 10 hours (sleeping, at the gym, having dinner etc) it sets you (and it makes everyone look bad) up for calling in fatigued. The company is trying to head the issue of calling in fatigued off before a trip is booked by knowing who is rested enough for the trip. Most of the time it works pretty well IMO.