Multiple Transits in China

What if I have multiple layovers to Beijing, during the same week? Am I able to use the 72 hour visa if my first layover in PEK is 10.5 hours, and then a week later I return to the US and have a layover in PEK for 7.5 hours?

My flight is the following
Depart US on Sat, 22/11/2015: USA - PEK (layover 10.5) - Japan (arrive)
Depart Japan on Sat, 28/11/2015: Japan - PEK (layover 7.5) - US (arrive)

Can I use the 72 hour free transit or do I need to apply for two 24 hour G-type entry permits?

-Isaiah