And too, at times even the FAA didn't know what was and was not duty time. The company for a while said that if you got 24hrs on a layover, it met the requirement for 24 in 7. The FAA hemmed and hawed for a while looking the other way until the issue was pressed and then the FAA said, "Nope.. it is not time OFF...it counts."
Us, FedEx, UPS and Astar use that all the time. We and Astar have trips that are up to 8 days in length. FedEx and UPS have trips that are two-weeks long. All have layovers of more than 24 hours to provide the required 24 in 7. Between the four airlines we cover Supplemental, Domestic and Flag ops.