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In video the time stamp in left upper corner is 3:01 PST. On USGS the earthquake time stamp is [M 5.1 - 7 km SE of Ojai, CA] 2023-08-20 21:41:00 (UTC) or 2:41 PM PST. Don't know if this was the first alert or not. It looks like it took 20 min to send the warning. Never have heard of an earthquake warning, this is not really a warning because it came after the earthquake, other than info warning about after shocks. 

Does the US have an earthquake warning system?
The USGS issues ShakeAlert® Messages but alert delivery will come by other public and private means (internet, radio, television, cellular), including Wireless Emergency Alerts (WEA) -- think of an AMBER Alert -- delivered by FEMA's Integrated Public Alert and Warning System (IPAWS).
https://www.usgs.gov/faqs/how-do-i-sign-shakealertr-earthquake-early-warning-system