I flew that flight recently, and I was able to do online check-in with boarding pass along with NRT connection to the US. I went to the check-in counter at around 10pm to collect my boarding pass since I didn't have a printer. No line-up.
As for earlier check-in, the other flights are all in the morning. NH954 flight to NRT departs at 8.25AM or NH174 flight to HND departs at 10.40AM. I'm not sure if there are any check-in staff around in the afternoon, since they're just contract workers at BKK.
I would just online check-in and drop off bags before the flight.