https://www.distance.to/ says all around one hour. Why don't you build railroads in America? Such short flights should not exist.
Nobody takes the plane for 30 min to get from city center to city center, we do it because we have to catch another flight from that city's airport and it's quicker by plane.
That being said, I don't believe the full SF->LA project is funded, and absent a more cooperative Federal government, it might never be.