I don't think the question was answered the way it was intended. let me offer another scenario. I deviate to HKG and fly from the U.S. to NRT in First because of the trip length. I elect to get a hotel room for the night and leave again early the next morning on a NRT-HKG flight that is 4+50 en route. Can I fly First on that second leg? In other words, am I on a continuous duty from the U.S. to HKG? If the answer is yes, how long would my layover in NRT need to be for it NOT to be continuous duty? Is there a written reference for this?

Thanks.