Bring a photocopy of your AP always saves your time

While you enter US, the immigration officer needs to make a copy of your AP for their record. It could take them 30 minutes to walk out of their booth, find a copy machine and make a copy. Bring one photocopy with you when you leave US because you can not get letter-size paper in China.

Anyway, it could take very long. Be prepared to be the last passenger to get through from the air plane.