USA Passport -> PRG - XIY (23 hours) - PVG (10 hours) - AKL

Hello! I was wondering - so I am flying from Prague to Auckland and have two stops in China. The first is in Xian which is 23 hours the 2nd is in Shanghai for 10 hours. I noticed it said the 72 hour twov you can only be stopping in one city, does that mean I can’t leave the airport for one of these stops because it will be combined over 24 hours in total or no? Can I get a 24 hour transit for Xian then another or the 72 or 144 (even though I am just there for 10 hours) for Shanghai? Very confused. Thanks!