Was going to echo other posters. You won't get there for kickoff if you leave at 6:00 p.m. on a weeknight. Traffic is terrible, particularly coming from (or anywhere near) Boston. You have to drive the gauntlets known as 93, 128, 95 and Rte. 1 in bumper to bumper traffic, then try to find an open parking lot, and hoof it at least 1/2 mile to the game. I am coming from southern NH down 495 and I am still a little worried that I cannot leave until 4:00 p.m., but I park a mile from the stadium and have never seen my lot fill up.
Good luck and have fun!