Tokyo - Beijing - Brisbane

I am currently in Beijing and have a single entry Q2 type valid for 90 days. My original return ticket was from Brisbane - Beijing, Beijing - Brisbane, but I postponed the return date and still haven't used my return ticket to Brisbane yet.

I want to go to Japan for two weeks, then adjust my ticket back to Brisbane so the departure time is within 72 hours. That way I can re-enter China without reapplying for a new visa. If my itinerary goes:

16 July: Beijing - Tokyo (with a stop over in Seoul)

29 July: Tokyo (stop over in Seoul) - Beijing - Brisbane (stop over in Singapore) am I eligible for the 72 hour free transit?