You should assume that you will have to go through immigration, bag reclaim and go upstairs to the check-in counters. This could take an hour if passport control is very busy, but you might get lucky and have it take less time.
Nevertheless, ask the Air China representatives when you check in for your initial flight as they may be able to give you definitive guidance.
In my transits through PVG in terminal 2, I have seen only a few airlines listed as having transfer service and I have never seen any staff working the transfer counters. I cannot recall if Air China was one of the airlines.