Vancouver to Beijing to Singapore

We arrive in Beijing at 2:10 on Tuesday, April 9, 2018 from Vancouver, Canada transiting to Singapore before 2:10 on Thursday, April 12th. Have I done the calculation correctly to qualify for the 72 hour free transit? Have read two different calculations on this - one states it starts when you land and the other one states it starts at midnight. Can you claify? Also does it cover a tour out to the Mutianya Great Wall? Thank you!