Best time to make it through Washinton DC?

OP has Millville as home base, which is in Cumberland County, midway between the Delaware River and Atlantic City - to get to I-76 and/or I-81 from where he is would not be very straightforward. That part of NJ has little in the way of fast thruways anywhere - Millville is a good 45 mins to an hour just to the Delaware Memorial Bridge, I-95 or the NJ Turnpike. From farther north in Jersey where you can get to I-195 and across the Delaware at the PA Turnpike, it's different but from down south, it's not so cut and dried.