When I flew this in June (and just about every time I flew this flight), there were no other flights being processed at Immigration and Customs. Immigration took 5-10 minutes and luggage took about 10-15...

As you're in J, it should save you a lot of queuing time at Immigration...

Just make sure you fill in the Immigration card correctly and completely. I've seen many times that those who failed to fill in the card correctly got sent to the back of the queue, i.e., when the queue got huge when the economy passengers join in...