The Hilton Narita has a small printed schedule available at the hotel. The bus to the airport is quite regular; many few stop at the nearby Narita Excel Hotel Tokyu, others are nonstop. The hotel shuttle schedule between the airport and the Excel Tokyu (which includes the Hilton, and is operated by them) is
here, actually quite easy to find with Google using
Hilton Narita shuttle schedule as the search terms.
The shuttle downtown is perhaps half-hourly. It might be someone has the specific schedule, but this is all the information I have from my several stays there.
Have a good stay.
