We're coming in from the left coast. When should we plan on getting in? The morning day before? The afternoon day before? The evening day before? I want to lock in the flight before the prices creep up.
If you haven't done tourist things in Philly before, come in on Thursday and devote Thursday night and Friday to seeing historic things, eating your way through Reading Terminal Market, enjoying the great restaurants and hitting all the Friday A-N events. Depart Sunday. Helps with jet lag and gives you a full play day on Friday.
If you are feeling adventurous, don't rent a car. Take the train from PHL and stay in a Center City hotel. Train to the game with all the families and fans. Walk everywhere else, great excuse to have cheesesteaks. It's well-marked and easy to figure out. Locals are happy to help.
http://www.septa.org/welcome/airport.html
Here's a story from a few years ago, which describes the game day trains
https://www.google.com/amp/www.phillymag.com/news/2015/12/07/septa-army-navy-game/?amp=1
Any hotel doorman or front desk staff can get you smart on the trains.
We have often stayed at the Philadelphia Marriott Downtown on Market St., which is centrally located for all the things we walk or train to. Using that as a place marker, you can find hotels at all price points in the same area. I think we walk a block or so over toward City Hall to catch the Broad St. Line to the game. DH is a Philly native who went to St. Peter's School nearby as a boy; I just follow him.
Consider doing the USNA Alumni Assn tailgater, which is usually in a hotel, for a big pre-game feed. Or, maybe your local Parents Club is tailgating in the parking lot.
https://www.usna.com/tailgates
Typically, one large hotel is the Army HQ and another is the Navy HQ, where the leadership stays. It's one big moving mass of Navy and Army spirit gear, so don't worry about where you end up staying. Book early, same theory as your airfare. Many hotels will have a two or three night minimum that weekend, and it won't be cheap.