It took us 15 hours to drive, and 2 hours to fly from BWI or IAD. If you're driving, it goes without saying to leave early enough to avoid DC area rush hour. From Baltimore, I'd leave no later than 4:30 AM.
If you are willing to fly, we have always been able to get great prices, although I'm sure that will all change now. I've never paid more than $150 for a RT.