Isn't the problem that the HND runways are already max'd out during "normal" hours with domestic flights? That is, allowing long-haul int'l flights to use HND during the day would require that some domestic flights be restricted or moved elsewhere? If so, where would they go? NRT?

The way I see it, the big advantage to the late-night, early-morning HND int'l flights from the US is that they significantly reduce the overhead of dead time required for business travelers.

Let's take the example of a NYC-based businessman that has twp days of meetings in Tokyo, all day Wednesday and Thursday. With the current NRT flight schedules, he must depart JFK or EWR between 11am-1pm on Monday in order to arrive NRT on Tuesday afternoon. Then he makes his way into town and checks into his hotel in the early evening, and is ready for meetings on Wednesday morning. Then, best case, he has to stay in Tokyo Thursday night and departs Friday morning from NRT, arriving in NYC around noon on Friday. Basically, the entire week is shot for 2 days of meetings in Tokyo.

Compare this with the HND schedules: Depart NYC Monday evening, after a full day's work on Monday, and arrive NYC Friday early morning, allowing a full day's work on Friday. Only 3 days away from work in NYC instead of 5.