As Greta mentioned, the National Press Club 5k is also on Saturday, at 8 a.m. This is a mostly flat course along Pennsylvania Avenue in downtown DC, followed by a sumptuous pancake breakfast in the press club ballroom. I plan on running both the 5k and the Rockville Twilighter 8k that evening.
(Note that you can buy a ticket for the breakfast separately, if you only want to eat and don't want to run. It's $11.24 for breakfast, which is competitive with Morty's. The proceeds presumably go to benefit literacy, or puppies, or something along those lines.)
Online registration ends Wednesday night at midnight, but if you miss that you can still sign up on the spot. If you do enter the race, put "GRC" as your team name. If you've already signed up, it should still be possible to run as part of the team if you email the organizers -- but if not we can sort it out with them on race day morning. Sorry for the late notice on the team, I have to admit I only signed up tonight myself. Hope to see you there!