Confused over Layover Time

I am planning to fly from Delhi to Nanjing via Beijing on 19th of June and return on 2nd of July through Air China. The layover time in PEK is 2h 50m in the first case (DEL-PEK-NKG) and 1h 30m in the return leg (NKG-PEK-DEL). Is this enough time to clear customs and immigration?

Thanks :)