It's always....always best to arrive the day before; get the '' flight from home'' stress out of the way, THEN a good night sleep., then you're ready to board asap, noon-ish and start enjoying your cruise, already relaxed.
IF THAT is not possible, then, 12.30pm arrival SFO, allowing for '' usual'' hassles following deplaning, would put you at the pier by 2.15pm, approx. It's about 30-40 minutes by taxi and mid-day traffic is not as bad as later//earlier. So, yes, you can make it....but the time you'd arrive at the pier is same time as about 60% of your cruise mates....lines do get frustrating in that time window. That is, IF the flight is on time to start with.....