I don't know of any actual regulations limiting physician work hours in general or emergency physician hours in particular.
From a labor law standpoint we are exempt from most state overtime and hours regulations because we are graduate degree level professionals (assumed not to need protection by the law from predatory employers🙄) and/or because many of us are independent contractors.
From a safety standpoint overworking yourself will lead to errors. My feeling is that you can't effectively work a load of 2.5 patients per hour for more than 12 hours unless your paradigm is really unusual (eg. you have midlevels, scribes, discharge planners, admission coordinators, etc. working on every patient with you). If you're trying to do 24 or more you really need to have some protected sleep time, say 4+ hours in each 24 of uninterrupted sleep, to be of any use.