If we're in port 8am - 10pm, how soon can I get off the ship?

[thermal]

I'm planning to do a Pacific Coastal cruise with Princess this April, and the schedule says we're in San Fransisco from 8am to 10pm.  

 

How soon can I realistically get off the ship?  I'm interested in booking a ferry to Alcatraz Island and am wondering what's the earliest ferry I could book (ferries start at 8:40am and go about every half hour).  It looks to be about a ten minute walk from the cruise terminal to the ferry.  

 

Thank you kindly.  

[cjpj]

Depends on docking, customs, tours, etc. I'd give myself at.least an hour buffer.

[skynight]

Previous port is a US port? Then no immigration. if that's the situation maybe 30 minutes after docking.