Depending on the kind of Japanese you're looking for (sushi vs. ramen vs. teppanyaki, etc.) and how much time you have, Gyu-Kaku might be interesting option. There are two around the Hilton but not that close: one on 44th St. between 8th and 9th, one on 3rd Ave between 49th and 50th.
I believe they have both a lunch menu and a happy-hour menu (pretty good deal imo) during Sunday lunch. If I were to eat til I explode I'd say I'd spend $60-70 on food there, but most people will be happy with a $20-25pp portion. Their green tea mille-feuille is from Lady M which I quite like as well.
Do you mean the Hilton on 53rd and 6th Ave?
What's their budget? I assume fairly low given that they are students? How much are they willing to spend per person, for food only (before tax, tip, beer/wine/drinks)?
Is this for a weekday or a weekend? Soon? The holiday season in NYC means that a lot of restaurants are very, very busy.
Ten is a big group, and some places won't take a reservation, though they may be willing to make an exception if you ask. Or at least call ahead that morning.