Originally Posted by YuropFlyer

IF the US government hasn't collapsed by then, and Visa-free entry for US citizen revoked by that date ( ), then you can only do 72hrs visa-free entry in PEK if you're NOT having a Chinese domestic flight. With 2 airports, you can only stay up to 24 hours. (general rule, a few special cases exists)

Given you said you'll fly via Chengdu, I don't understand if that will be on the flight out of PEK, where you want to spend >24hrs before, or when you come back. If it's when you come back, note that the time from touching China to leaving China has to be <24 hours. So, touchdown in Chengdu at 2pm on Day1, flight to Beijing, spending time there, departure on day2 has to be before 2pm.