I concur with 2 hours minimum.

Recent experience last month (this is best case when everything fell into place. I was specifically timing this as I've done this connection in the past a couple of times):
06:03 HND wheels down
06:12 at gate
06:15 deplane (from front Y in a 788)
06:19 completed immigration/customs (I had ABTC - no wait). Ran all the way to immigration (long)
06:21 at bus platform #5 . I bought ticket at kiosk
06:30 bus departs
07:37 Terminal 1 South Wing
07:50 NRT airside. Used Star Alliance fast track for security and ABTC for outbound immigration.

Only carry on and all BPs procured

Immigration inbound at HND is the big variable - lines can be long in the non-Japanese line. Immigration outbound at NRT has fast track (at least for Star Alliance) and from my experience, relatively quick in the early mornings.