International flight with Two Stops in PEK and CAN.

I am trying to travel from Los Angles, CA to Hanoi, Vietnam. The flight I am trying to book has two layovers in China. The first is in Beijing PEK and the second in Guangzhou CAN. The connecting time for each layover (PEK>CAN and CAN>Hanoi) is two hours. Will that be enough time to go through customs and get our TWOV permit stamp?