Can I use the 72 hour visa in both directions of flight?

I am from the US (US passport) and on a business trip in Taipei. I plan to fly RT from Taipei to Hong Kong. I connect through Shanghai Hongqiao Airport in both directions. Can I use the 72-hour visa free transit in both directions? Is there a certain amount of time that I must stay in Hong Kong before my return flight in order to use the 72-hour visa free transit again?