Visa. Am I eligible for 24 hour visa-free?

Hi, I am an American who will be travelling from the US to Vietnam via Beijing (first entry - 2.5 hours connection time) and then Guangzhou (about 3 hours connection time) to Vietnam. On the returning trip. I would have about 6 hours waiting for my Guangzhou to Beijing flight, and then 2.4 hours for my Beijing flight to US flight.