If you want quick trip to Xian to just see Terracotta Warriors can do one day no overnight on weekday go PEK/XIY Air China Flt#1203 Dep7:30/Arr9:15, Return China Eastern Flt#2105 XIY/PEK Dep17:40 Arr21:10. You can arrange land portion in XIAN with CITS(China International Travel Service) in USA or when you get to PEK