Even with "walk off" you'd still be cutting it pretty close. We sailed on the Diamond in October and went through customs at San Pedro. Lines were long and moved slowly. If you have the option of a flight after 12:00 noon, I'd book that and pass on the 11:00 flight. We didn't do walk off, but had red tags (1st group off the ship). By the time we found out luggage, went through customs, boarded the transfer to LAX, went through screening at the airport, we had 30 minutes to spare before our noon flight.