Yes I agree, That's why I said it takes around 15-20min to go between A and C because of the poor transit system at IAD. With boarding about 30min or so prior, that doesnt leave any time. If I arrive at IAD and VDB to take a later flight, then I have plenty of time. However, arriving 10-20min prior to boarding may be too late since the VDB seems to be in order of first come first serve. The flight out of CHS is the last 1 stop routing of the day. The flight out of IAD is the third to last direct flight. Therefore I am not considering VDB in CHS as an option.

Anyways, my basic question has been answered. Thanks