Their online appointment doesn't work, so yes, you have to show up early. I showed up at 7am on Friday and the line was long and around. However, they gave us a slip with a time to return that day. The paper slip was acting as your appointment only for that day.
If you don't have an appointment then my answer is yes ,you do have to show up 4am in order to be seen as soon as they open the door and you will be out before 9 am. If you want to show up by 6 or 7 am you could but you will be out of the DMV by 2 or in the afternoon ,so it's your call
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