SFO to Shanghai with Shanghai to Hong Kong in the middle

Hi, I am flying round trip from SFO to Shanghai for a week. Then in the middle of that week, will take a round trip flight from Shanghai to Hong Kong and stay for 2 days. 2 seperate flights. The time in between flights will be less than 72 hours. Is it possible to use the 72 hour non-visa stay on both times that I am in Shanghai?