72 hours free transit: Mexico-Shanghai-Honk Kong-Shanghai-Mexico

I have a round trip ticket Mexico-Shanghai. I already got my one entry chinese visa. I was planning to travel for 15 days only into China continental cities, but after I got it I decided to stop 2 days in Hong Kong at the end of my trip then travel back to Shanghai to get my flight back to Mexico. Can I enjoy 72 hours free transit to go out Shanghai airport to sleep in a hotel and get back next morning to take my flight back to Mexico?