Boarding a cruise ship in Tianjin

We are Australian passport holders boarding a ship in Tianjin departing port at 1800 hours on 17 October 2016. We understand that there is a 72 hours visa free stay. Do we need some form of documentation to show on arrival at the Tianjin airport besides our ship the Golden Princess's boarding documents.
Since we board the ship at about 1300 hours and the ship departing at 1800 hours, will the 72 hours free transit include the time after we board the ship or when the ship departs from port? We would like to see as much of Tianjin as we possibly can and do not want to be caught short, we want to be clear about this. Thank you