I'm traveling SYDNEY-XIAMEN-SHANGHAI-HONG KONG, do I need visa?

Hi,

I arrive in Xiamen at 6:50pm Friday, then have my connecting flight to Shanghai on Saturday at 8:00am (SYD-XIA-SHA booked as one ticket) and then plan to fly at 6:30pm on Monday to Hong Kong, so will be in China for less than 72 hours. Is this ok on a 72 hour visa exception?