What time do the Star Guardian Skins come out?

Is there a specific time Riot releases new skins? Because on the patch notes it says "September 12th", not the exact time. Do they drop at Midnight (PST) or does Riot wait until closer to morning to release them?
Best New

We're testing a new feature that gives the option to view discussion comments in chronological order. Some testers have pointed out situations in which they feel a linear view could be helpful, so we'd like see how you guys make use of it.

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