Whether you're from the New York area or are a visitor, an excursion to West Point is well worth a day.
I would strongly recommend the two-hour tour that includes visits to the cemetery and chapel as well as other campus spots. The guide was informative without being overwhelming and included many stories about important graduates and the history of the academy. There are other tours, so check the web site to see which suits your time and interests. You should also leave time for the Visitors Center and Museum, which will add to your understanding of the academy and military history.
The setting on the Hudson River is beautiful, so you might want to leave time to walk around the area and to have lunch. There are also many other historical sites in the area if you are a history buff.