There's no need to arrive too early; about 20 minutes beforehand is fine. Even if you don't arrive at Pier 33 early, as long as you get there before the boat departs and exchange your ticket, you'll be fine. You'll need to go to the ticket booth first to exchange for a physical ticket. Once you arrive, you can explore on your own following the suggested route, and there are also audio guides available in various languages. After completing the Alcatraz tour, you can walk to the pier to catch the next available boat back to the bay. Upon returning to the bay, you can walk to the ticket exchange point at Pier 39 to continue with a one-hour bay cruise. Please note that the QR code for this ticket exchange will be sent to your email, not the Klook QR code. You can choose your preferred cruise time when exchanging your ticket. The cruise will take you under the Golden Gate Bridge, allowing you to admire the bridge from a different perspective.