72 hour vs 144 hour transit visa

We are flying from the US to Hong Kong to Shanghai and on to Japan. We are scheduled to arrive in Shanghai at 12:10 pm on June 27th and fly on to Japan June 30th at 9 am. So we're thinking that we are under the 72 hour rule. However, should we apply for the 144 hour visa free transit just to be on the safe side? Thank you