Given the amount of time you have I would jump in a cab just to be safe. Its about $14.00 door to door and its alot less stress if you have luggage and your dealing with the rush hour commute. It wont take you more than 15-20 mintutes to get to DCA. Unsure if your Elite, but the elite line will save you a good 10 minutes in line at that time of day.

I like Metro if I have plenty of time to spare and its on my own dime. Otherwise if the company is paying I always take a car service or cab.