Does 72hours visa free work when have one 72h in Guangzhou then 1 transit in Beijing airport?

Hi, i'm a French citizen. As I did before, I can have a 72 hours free in China when I'm in transit. but can i stay 72 hours in Guangzhou and fly to Mongolia while I have to transit via Beijing? Meaning I stay within the Beijing airport, just wait for the flight to Mongolia. Indeed there is no direct flight from Guangzhou to Ulaanbaatar. But. I want to spend time in Guangzhou this time, not Beijing. Can you answer if this works or not?
Thanks,
Aulan living in Vietnam