Hi, I am a US citizen and i am in guangzhou Now With a visa for china for 2 entries

in 2 days i am going to Hong Kong for a full day then I am going to spend 5 days in Guangzhou and then I will leave to go to Vietnam and Cambodgia, after this tour I have to come back to Guangzhou to take my plane back from Siem Reap to Los Angeles but I am going to stay 2 days in Guanzhou. Can I get the 72 hours free transit for my last 2 days???