Do I need to get a two entry visa or can I qualify for the 72 hour free transit?

I am travelling from Canada to Shanghai and staying there for two weeks. My ticket for that portion is for Canada-Shanghai- Canada. While I am in Shanghai I will travel on a separate ticket Shanghai-Bangkok- Shanghai. I will arrive in Shanghai from Bangkok at 6:00AM on april 10 and then depart Shanghai for Canada at 15:55 April 10th. Thank you