Note, effective immediately, TWOV rules have changed to increase the total allowed time in some Chinese cities.
For Beijing (PEK), Chongqing (CKG), Guangzhou (CAN), Hangzhou (HGH), Shanghai Hongqiao (SHA), Shanghai Pudong(PVG) or Xi'an (XIY) the 72-hour period is now calculated from 00:01 the day after arrival.
This effectively gives you another day to explore those cities if you arrive early on the first morning.
Other chinese cites (Chengdu (CTU), Dalian (DLC), Guilin (KWL), Kunming (KMG), Shenyang (SHE)) have retained, for now, the 72 hour period in calculated by scheduled arrival and departure.
24 hour TWOV is not affected by these changes.
As always, refer to TIMATIC for the latest visa information.