The FAA doesn't care how much rest you've had unless you're acting as a flightcrew member. You could work a full duty day, then the company decides they want you to vacuum the floors in the crew lounge all night and the FAA couldn't care less -- that's what a contract is for. Unfortunately, at ASA, we have no contractual protection pertaining to a max duty day if the last leg is a deadhead. As long as you don't touch the controls (or radios or whatever) without at least 8 hours of uninterrupted rest in the previous 24, you are not violating any FARs.