We are renting a car when we arrive in San Francisco and taking it to the Fisherman's Wharf area to explore for the day. Then we will drive to Napa- time is flexible but would like to be there before dark. We realize the Golden State Bridge is heavy with traffic, but would there be a "best" time to cross it. We want to see it and it sounds easier going northbound at the beginning of the trip rather than southbound at the end. Is the "magic" time 7:00 p.m.? Thanks for your help!