FLIGHT STOP in TWO CHINESE CITIES

I am travelling from US to Tokyo but has a layover in Beijing then Dalian. My Return flight would be Tokyo to Dalian to Beijing then to US. However I have an 18 hours layover in Beijing, on my return flight, do I need to secure a transit visa if I decided to tour Beijing on that 18 hours layover, or am I entitled of the 72 hour free transit. Thank you