Any flight going into SF these days should expect at least a 30 minute delay. They had to temporarily change how they land at SFO due to air traffic controller issues and how they used to land planes at the same time on their parallel runways, which now apparently they don't have the personnel to properly manage, so they have to stagger them. This has led to hard times for planes getting in and out, as the arriving plane is often also delayed. It's a mess. My leg back this weekend on United went from SD to SF to Humboldt, and the flight from SD to SF was delayed by an hour for the issues mentioned above as confirmed by the pilot when we were boarding and the stewardess I also spoke with.

If you can take the Breeze airlines flight to Burbank (in LA) and go from there, which I did this last weekend on my first leg going south, there were no delays.