Shanghai to Xian on 72 Hrs Transit

We will arrive Shanghai on Dec. 16 at 5:35pm staying in Shanghai hotel, outbound flight to another country on Dec. 18 at 7:20pm.
My questions are:
1. Will we have enough time to visit Xian to see the Terracotta Warriors?
2. Will the 72 hours transit waiver visa allowed us to travel to Xian on a US Passport?

Thanks in advance for the help.