Ferry ticket from Sorrento to Capri

Hi, Giangilberto from Milan, so the times match the actual duration of the crossing so it's almost certainly the arrival. But do one thing before paying. Check that only one one way ticket is shown in the cart and not a return ticket. You can check it very quickly. As for the account on the majority of ferry sites in Italy you almost always buy as a guest without registering. If the form gives you problems, skip it. You should search and there should almost certainly be an option that says buy ticket as a guest without creating an account. If unfortunately this doesn't work either, in Sorrento you can also buy tickets at the pier in person on the same day of departure. Let's say that on a busy route like Sorrento, Capri in September is not a risk. One thing to keep in mind: since these are two separate one-way tickets, your return is tied to a specific time and if on that day there are problems with bad weather, for example, usually there is a Libeccio that could blow very strongly.
The ticket bought at a fixed time could become a problem. There is a risk of rough seas and strong Libeccio winds, this can cause significant ferry delays. Usually, fast services using smaller boats get cancelled, while slower services using larger and therefore more stable vessels continue to run.

We took a ferry last month from Sorrento to Capri and Capri to Naples. I did not purchase in advance because I didn't know if I would make it, or if I would want to go earlier or later. There are plenty of ferries. No need to purchase in advance.

You just purchase the ticket at the dock the day you go.

There are likely to be more than one company working at the Sorrento dock. "Macy's" won't tell you that "Gimbell's" has an outbound ferry in 20 minutes, while theirs is in 40 minutes! Do have an idea of the last 3 boats home schedule, because they are likely to "suggest" a particular departure for your return. I would never plan on the last boat of the day.

I looked and like Giangilberto said, that's just the time you arrive on Capri.

You will see there are other faster and cheaper ferries available around that same time on other lines. I'm not really sure about the necessity of booking in advance. That's a busy time of the year but there are a lot of ferries. We booked ours the night before.