I know this is "Late" to this thread, but we have made the trek a couple of times now. However, we have done it towing our camper, so we have sleeping accommodations with us. That being said, We will leave the evening after work. (typically a Tuesday) with the objective of getting PAST the DC Beltway. (As others have said, it is a disaster even at that late hour, just not as bad). We have stopped twice now in "Ashland" Virginia for the night. There is a nice truck stop right off the exit, and in the AM there is a Cracker Barrel where we get our breakfast. The next day we do a "Power Drive" to get almost all the way to Fort Wilderness (where we stay). We have stayed in the last rest stop in Georgia for the night and we have also stopped at a rest stop about an hour from WDW. Either way, we get up in the AM (Early) and get into the Fort and get checked in and go about our day.
Going home we do the reverse except we typically do it in about a day and a half as opposed to almost 2 days (depending on how I feel as I am the only one driving it). Again, as mentioned, the DC Beltway is HORRIBLE. The one year we were coming back and hit the beltway around lunch time on a Sunday and thought it would be okay. WRONG! I think it was worse than a Monday Morning Rush hour. Last time we went "Around" the beltway. Don't remember the exact route, I just let the GPS handle it.
So really the best advice I think you can get is to avoid the DC Beltway.
(PS, I come from Plymouth PA)