I've only had one time where the line was crazy long, and that was at breakfast.
I passed by on the same day later in the day, and line was pretty much nonexistent.
Flo's is one of the few places in DCA that offers a real breakfast, so breakfast lines can get long, especially because it is so close to Radiator Springs attraction.
At the time, I didn't know Whitewater Snacks at GCH offers breakfast too, or I would have gone there.