We're talking US/FAA FARs; Note that all regs 91.1001 through 91.1443 are under Subpart K - Fractional Ownership Operations. If you're not under one of those, like Netjets or others, those regs don't apply. If you operate strictly Part 91, say a corporate pilot in the company's privately owned aircraft, then there is no rest/duty hours requirements. That said, if an incident or worse were to occur, the FAA could use the general 91.13 Careless or reckless clause against a pilot. Also, if you're talking about 135 and 91, yes, you can legally "time out" your 135 duty period, then fly (an empty) plane under 91, say to return to base, for as long as you might wish. But, you'd have to satisfy 135 rest period before being assigned another flight.
Most decent Part 91 flight departments would have their own ops manual, providing reasonable duty/rest guidlines for the sake of safety. There are abuses, of course, and in that case, my advice would be find another job.