I arrive to Xian at 23.55 for 72 hour visit. What are the opening hours for the permit?

Jorgen, usually, there is a transit counter which is open till the last flight arrives or departs. You need to inform the airline that you want to use the 72 hour free transit before you board the plane. After arrival, you should go to the transit counter to apply for the 72 hour free transit and then get the free stay permit.