On a Saturday, I'd say give yourself 30 minutes before the time you want to arrive at the airport. And don't forget to get a flat rate voucher -- they have them at the bell desk
I would leave at 11:15. Been doing it multiple times per year for over 10 years and have never encountered an issue. Sat. should be fine that time of day.
Last Friday at 10am it took us 22 minutes to get to SNA from DL. We fly Southwest in Terminal C and there seems to never be a line at security. We generally leave DL 2 hours before our flight, just to be safe. We had over an hour to have lunch last trip in the airport and we had to also had to return our rental car.