I am in agreement with Mike. We did the same cruise and the bus is waiting for you as soon as you get off of the ship. You get off the bus at the border and then walk thru the Immigration building and get back on the bus. You do not have to take your luggage thru Immigration. The bus then takes you to the San Diego Airport.
We live in the So. Calif. area and we took the train which is a short cab ride from the airport.
Have a great cruise as I know you will. Don & Jennifer