Feb 27 gathering is from 5pm till 6:30.
OK, and...
Rush hour in DC is a new experience for those who've never seen it.
Metro makes a sardine can seem empty.
Parking is still expensive (would cost $20-$25)
Traffic is gridlocked, particularly for people who don't know the tricks.
People who come in early to beat rush hour will be long gone. People who come in late to let rush hour pass before leaving won't be off work yet.
Conservatives generally work. You can't expect maximum participation on a weekday in DC. Period.