Although I no longer live in DC, I would travel to Florida many times a year. After many trials, I found that leaving DC (or passing through) at 4 AM would eliminate ALL traffic and I would miss rush hour in the DC area as well as Richmond (not too bad, but bad enough). It actually became a relaxed (if you can imagine that) trip. Since I usually would drive through to NE Florida in 12-13 hrs, I also avoided rush hour in Jacksonville.
When returning I would leave NE Florida 10-11 AM and be back in DC for the evening news and again avoiding rush hour in all cities.
BTW, I quit doing this 5 years ago and I always used I-95.
Paul