Check-in at HND must be completed 60 minutes before departure (assuming standard check-in timing), so that makes it 3 hours from last plane to get to HND.
Quick check myself - I haven't looked at the other options - but from NRT to HND via, say, the Keisei line train (direct service, it says) will take around 90 minutes or thereabouts. That's without any other waiting time (i.e. line up with the timetable). Apparently a limo bus should take around the same amount of time (the bus is naturally more frequent).
This cuts any other auxiliary time down to 1.5 hours.
In my experience, NRT immigration doesn't take too long. There is no priority, but they do work pretty quickly as long as you don't mess around in answering their questions. Just don't dawdle to the passport control!
Only thing that may upset your plans is delays, but then it is one ticket so you have some protection (in theory). In this case, you may be able to resort to staying in NRT and negotiating with SQ / NH directly there rather than hike out to HND. (If they tell you that you can make it, off you go!)
Not the thinnest of connections, and makes a nice story to relate over a drink when you get home