Because of coyotes and a mountain lion that visit that area, I advise not visiting "any time" because visiting during the night will be dangerous.
It's free to access and is open the same hours as Griffith Park. I believe it's 5:00 a.m. - 10:30 p.m. per the City of L.A. website.
It's literally like a park where you just walk up the stairs and bam! You see it
It is free entry and you should be able to go in at anytime.
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