If you received an LOE and are serious about attending, I recommend doing an overnight visit as early as possible. You will get a feel for what cadet life is and more importantly you should have an opportunity to meet with someone from admissions where you can further reinforce your interest and you could pick up some tips on where you might need to tune up your application. Your visit also demonstrates to your MOC that you are interested and their nomination would be appreciated and not go to waste.