Every time I've flown into NRT or HND, it is relatively quick to get through. It's been less than 30 minutes. Have the Japanese government stuff already filled out online and be ready to show at immigration so you don't have to stop and fill out paper forms. The time you take waiting to get through immigration is about the time you need in waiting for your luggage to come out. I normally come out and the first bag is still a couple of minutes away from coming out. You can use any open customs line for bags.