Sydney to Beijing with no visa

I am arriving in Beijing at 13.25 Wednesday morning, does the 72 hour free transit ends on Friday or Saturday? I am hoping I can fly out Saturday at the latest and be able to enjoy nearly 4 days in Beijing.
I was not aware that I needed a visa, after doing some researching i believe I can get a L type in Hong Kong at the airport. This will have to be my next flight.