No, they operate on first come first basis till their parking space gets full with maximum allowed capacity.
No you don't have to have a reservation. But I implore you to to leave early from wherever you're staying or coming from and get there at least 30 minutes before they open the gate because they do fill up fast and they will turn you away no matter how far you came.
They fill up fast and due to covid they are not operating at maximum compacity
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