Flight comes back to Tokyo before it leaves for a third country, do I qualify for a 72 hour visa

I am a US citizen and am going to Tokyo on a Business trip and would like to visit Shanghai for three days, my flight can be from New York to Shanghai and Shanghai to Tokyoa and back to New York. Under this circumstances can I use 72 hour free transit to visit Shanghai.

Second option is on my way back from Tokyo, I come back via Shanghai and take a break in Shanghai, but the trouble here is that Japan airlines flight from Shanghai comes back to Tokyo, before coming to New York, so I am not leaving for a third country from Shanghai? would I qualify for a 72 hour transit?

Is is possible for me to just go and come back from Tokyo to Shanghai for 72 hours while I am in Tokyo?