Can I use the 72 or 144 hour visa?

I am traveling from Singapore to Shanghai then Shanghai to the United States. I am flying Delta the whole way and they use China East as a co-share airline. I fly into Shanghai on the 18th and out on the 21st. Can I use the 72 or 144 hour visa? If so, am I correct to understand that I tell Delta when I board at JFK on Dec 6 headed to Singapore? Am I also right to understand that I will get the Visa in Shangahi with a valid passport? There is nothing I need to do before leaving?