2 beijing questions

Hello - I am looking at flying into Beijing at 15.20 pm arrival on Sunday March 11th and leaving at Wednesday March 14 at 20.40 pm (this is 77 hours from the arrival flight technically) So is this not allowed for Beijing as it has different rules than rest of China? Also, if I decide on one of my days to fly to Xian from Beijing for 1 day, is this allowed?