Little confused about correct way of booking tickets, does it have to be 1 return ticket????

Hi, If I book a flight Birmingham to BJ and return Tokyo to Birmingham as one transaction. Then after this separately book a one way ticket from BJ to Tokyo which will depart within 72 hours after arriving in BJ. Will this be acceptable for 72 hour free policy??

I am unsure, as some places like air china and Chinese embassy sites make it sound as though you have to book 1 international return ticket in one go which has a long stopover i.e. 32 hours etc.. only then you qualify