Originally Posted by jpdx

In the last couple months, my extremes were a 70 minute immigration wait at HND around 6pm (NH212 from LHR) and a 0 minute immigration wait at KIX around 11am (AF292 from CDG).

IME, unless you arrive at off-peak hours or fly into secondary airports like Sendai, the wait is completely up to chance, just dependent on how many planes arrived before you. I've waited >an hour at NRT, HND, and KIX several times, and I've been through in <5 minutes several times.

Interestingly, filling out the immigration and customs forms online and obtaining a QR code prior to arrival has taken extra time on both trips referenced in the first paragraph. At HND, customs was a complete zoo and the line (several hundred Japanese people ahead of us Westerners who waited forever at immigration) took 15 minutes to slowly snake to the customs exit. At KIX, there was nobody in the regular customs line, but exiting through the QR code path involved a 10 minute wait (not helped by the fact that at KIX, the setup for QR code verification kiosks is stupid -- complete after collecting luggage, on the way to the exit). I didn't have a customs card filled out and am not sure if you're allowed to go to regular customs counters when using the QR code at immigration, but I think it makes sense to fill out the customs form on the plane anyway to be prepared (at KIX, we were ultimately directed to a regular customs counter from the QR code queue, and waved through without customs form).

Perhaps worth noting that if you arrive at HND at a peak time, everything will have insane lines -- currency exchange, rail ticket counters. Best to have a Suica ready and head to Shinagawa to buy tickets for onward travel.