California Department of Motor Vehicles [CA DMV] review: appointment time

I arrived an hour and a half earlier than my scheduled appointment. As I entered and attended by the clerk I was told I had to wait until my appointment time before I can even get a number for service. Given that the process at DMV is not speedy I arrived early to get a head start on the lengthy process. I asked to speak to the manager and was referred to Window 4. The manager accepted for me to be serviced earlier. I asked if DMV had a written policy that clients cannot be serviced until their appointment time if they are early. She stated "no." I also witnessed another person being turned away for being 20 minutes early. DMV is a public entity and it's function is to provide customer service. If a policy is not in writing why are customer being asked to wait longer if they have an appointment. The office was not busy at all. I would like to know why DMV is having customers wait if they have an appointment and arrive early.