If somebody has issues driving thru Leesburg any time of the day, any day of the week, I suggest that they totally avoid 270-495 around DC.
and the worst part of I-95 is the section from Fredericksburg North to the beltway which should be avoided at all costs.
But any route can develop problems any time any day. My friend who routinely goes from Richmond to North of Frederick always drives the beltway. One time he tried "my" route 15/17 and said it took him several hours extra, which didn't make sense to me. Upon further review, he had made this trip at the time they were looking for the beltway sniper and all roads were clogged everywhere. Additionally he usually makes the trip North after work on a Friday, so things can be a mess anywhere.
My experience with these routes has been trips twice a month for 16 years. 99.9% of the time I have had no issues.
bumpy