Toronto connecting in Tokyo to Guangzhou, if I can get 72h free transit at the airport?

I will be arriving at approx 9pm and would like to make sure the customs office will be open at that time for me to get my visa? I am also wondering if I decide to fly directly into Hong Kong and take a car service to drive me to Guangzhou , can I get the 72 hour free transit at the border crossing or does it only apply if I fly into the airport. Also can you explain to me if I need to go to a local police station to get my 72 hour free transit stamped? It's is unclear about this. I will also be travelling with a Canadian passport. Thank you for your help.