The cruise terminal is really easy to get to. It is straight down the Embarcadero.
See https://sfport.com/maritime/cruise
Typically the scheduled departure time is 4:00 PM so if you are arriving at the airport at 10 AM it will take about 1 hour to get to the cruise terminal including time to depart the aircraft, etc.
Depending on how fast the ship has been cleared boarding should start around about 11 AM. If you arrive prior to your boarding group time typically you will be allowed to board. At least that has been my experience.
If you get on the ship during lunch time one of the Main Dining Rooms on deck 6 should be open for lunch.