How long does it take to reach the Fisherman's Wharf from the international airport?

You don't say whether you will be using a rental car or traveling by public transportation. It is approximately 30 minutes by car from SFO to Fisherman's Wharf if you know where you are going. There is now BART service to the airport and that would be a quick way to get downtown, from where you can take an Embarcardero train (Metro) to Fisherman's Wharf. You depart for Alcatraz from the Wharf, so it would be quite easy to book the trip and eat seafood before or after going to Alcatraz. This should be very doable.