Hmmm, no customs express lines at TBIT that I've seen. If you land on time, you should have time to make it to an AA flight that leaves after 11pm.
I've been in your situation, minus the transfer since I'm LA-based, and the 9pm international arrivals are numerous. You have to claim all your bags even if transferring. You should be through customs by 10pm max. If your bags are checked all the way to your final destination, coming out of customs, go RIGHT (sign says something like "TRANSFERS"). Up the incline will be an area to re-check your bags. Once they're on the way, exit the terminal to the right (WITH the flow of traffic) and walk the 100 or so meters to terminal 4.