Will be staying in Arlington in Aug and have Fri and Sat available for site-seeing with 12 year old grandson. Hoped to drive to Mount Vernon Friday Morning, spend about 4 hours there, then drive to the Udvar-Hazy Center. For Sat we would get timed tickets for the Washington Monument and visit some of the Smithsonian Museums. Given traffic and crowd conditions that time of year should we switch days for the activities? Also are we being too ambitious planning Mount Vernon and the Udvar-Hazy Center on the same day?