In the SF Bay Area, commuting by car over the past 15 years, I've found that there are no generalizations I can safely make about traffic during a particular time of day, which applies to all routes and all directions.
I became an early riser for a particular job and have stayed on that sleep schedule for (arguably indirectly related) health reasons, so I'm awake by 13:00 UTC every day, which is 6am or 5am, depending on Daylight Silly Time. However, I tend to adjust my commute departure time such that I get a good overlap of being in the office with my cow-orkers.
In my case, commuting is one huge advantage of waking up early, when I do it. Traffic between 5-7 tends to be far less stressful, even when it's heavy. These are all people who are relaxed, focused, and moving quickly without being in a hurry. 8:00-10:00 people are rushing and hurried and angry and chatting on cell phones, 11:00-13:00 gets very heavy with lunch rush, with some people hurrying and others just meandering along getting in the way. Then after a brief lull between 14:00 and 15:00 (the early risers heading home) you start getting a mix of traffic from commuters and people doing afternoon activities, which tends to persist until late (20:00-21:00) except on Monday nights, unless there is an event like a Red Sox game or something.