72 Hour Visa Exemption if I travel Siem Reap - Shanghai - Beijing - Tokyo?

I travel from Siem Reap to Beijing, with a 5 hour stopover at Shanghai.

I arrive at Shanghai at 4am on 18 October and will leave for Beijing at 9.20, without leaving Shanghai airport. I'll arrive at Beijing at 11.55am on 18 October.

I intend leaving Beijing at 8.45am on 21 October and flying to Tokyo. This is within 72 hours of arrival at Beijing, but over 72 hours since arriving in China.

Will I qualify for the 72 hour exemption?