Is vacation time the best time for the march?
A date after schools are out for summer might not be the best plan.
Many people might be away for their summer vacation or have other family oriented events scheduled.
Memorial day might be an option.
Although I am not in the US we are tossing around the idea of having a supporting march here in Ireland but dates past early June run into conflicts with peoples summer plans.
In all likelihood the DC march will draw disproportionately from the eastern seaboard with supporting marches popping up in distant regions so a weekend before schools are out might draw a bigger crowd.
Correct me If I am wrong but if the March was scheduled for a 3:00 start on a Saturday, people up to about 1,000 miles away would have time to travel by bus to get to the event.