Eligilble for 72 hour visa transit?

I am flying to Taipei via Shanghai from LAX.
I am a US citizen and I have an overnight layover in SHANGHAI for 18 hours and 40 minutes. I would like to see the night city of shanghai. Would I be eligible for the 72 hour or the 24 hour direct transit? If I am, do I need to go to the China embassy and apply for it? Or does that work once I land in Shanghai? Thank you.