Hong Kong, Shanghai, Los Angeles

I am in Shanghái with a valid visa for 2 entries. Next week I´m going to Japan and I will return to Shanghai (I will have no more entries left).

During the last week of my travel I want to visit hong Kong and then return to Shanghai. So my question is: can I apply for this 72 hour permit when returning from hong kong to Shanghai?
I already have tickets departing from Shanghai to Los Angeles.