I drive from SW balt to capitol hill for squash about 3 afternoons a week. The trip down the BW parkway to the club takes 45 min. about 35-40 min from bwi. crossing the 14th st bridge to va at 4-5pm is a zoo. I95 is ok, until you hit the dc beltway the north side, which is very ungood. you cannot get across the wilson bridge to va either. the 8pm guess is a good one as arrival at iad or dca will be closer to 7pm than to 6pm on a lot of occasions.
learn to love bwi.