Is there a minimum length of stay required in the transit-to country?

I would like to fly Boston-Beijing. One option is Boston-Tokyo-Beijing on one ticket, stay 72 hours, then Beijing-Toronto-Boston on another ticket. The stay in Toronto is ~2 hours - does this qualify? I could also buy separate Beijing-Toronto and Toronto-Boston tickets for the same flights so it is less obvious I'm only doing a layover in Toronto. Thanks!