I think there are people who still go to the Department of Motor Vehicles without an appointment. Because who doesn't like a good session of waiting in line? Lucky for you, Gene Ekster put together a simple time series that shows the average wait time throughout the day.
Data is from the the published wait times on the California DMV site. Although there's no mention of how the sample data was collected. From a common sense standpoint, and based on wait time in a lot of other places, the results make sense. There is less wait time on Wednesday and more on Monday. Go in the morning, and avoid 11am or later if you want to reduce your wait. Or just make an appointment.