If you're one of the family or close friends who is attending the wedding rehearsal today, you need to either be at the Hawthorn Suites by 2:30 for a chartered limo-bus ride over to Mount Vernon Inn, or be at Mount Vernon Inn itself by 3:30. Rehearsal is 3:30-4:30.
If you can't make the rehearsal due to travel and are just coming to the dinner, be at Place One, 5500 Holmes Run Parkway, Alexandria, VA by 5:30 or so. You will need to park either in one of the visitor slots for the apartment building (get a visitor pass at the front desk inside to put on your dashboard) or park at the Hawthorn Suites across the street (get a visitor pass from THEIR front desk in that case.) The meal is in the big meeting room on the first floor of the apartment building.