China Travel under 72 hours

I will be traveling from New York to Japan. On our flight home we fly from Tokyo to Nanjing, we stay in Nanjing for 16 hrs (overnight so we will book a hotel), the following morning we fly to Shanghai for 12 hrs, 8am-8pm and plan to leave the airport & spend the day touring Shanghai before we fly back to NY. Do I need a visa? Will a 72 hr visa work for both locations? Do I need to bring passport photos for any visa given at the airport?

Doria Paci