The "midori-no-madoguchi" or Green Window office is open until 11:00 pm but the last Haruka Express leaves shortly after 10:00 pm. You will find it in the Access Plaza across the street from the Arrivals Hall. After you come out of C&I and get money, etc., go up the escalator to the 2nd floor and cross the street via the elevated passenger walkway. There are 3 bridges, all connected on the other side. Use or cross to the center one and continue into the walkway toward the Nikko Hotel. The JR office is on the left before you get to the hotel. Look for the glass-walled office with green trim (thus Green Window.) The wickets to the platforms are on the right, directly across from the ticket office.

Don't sweat finding it. The airport is well signed in English. You will see plenty of directional signs to the JR Rail Station with train symbols. It is hard to miss.

In case you are interested and have time, there is a tourist information center (TIC) on the 1st floor, against the opposite wall from where you enter the Arrivals Hall. It is kind of hidden at first behind the stairway. I think it is open that late and you could get free information about your destinations. On the other hand, you may want to just hurry across to get in line at the train station as there can be a long wait to exchange rail passes or buy tickets if you let the crowd get ahead of you. YMMV.

JR