Cinque Terre ferry tickets.
 

How early (or late) should you purchase tickets for the local ferry from Portovenere.

We just did ours (a few weeks ago) from the stand at the ferry landing about 5 minutes before it left. I think we took the 9am ferry, but I don't remember exactly.

I don't think they have a computer booking system for the daily trips, so you just buy a ticket before getting on the boat. The boat operators' web site gives details of the boats, and you can see that most of them carry between 250 and 350 passengers, so there will normally be plenty of space.
http://www.navigazionegolfodeipoeti..../la_flotta.php

On the spot--take the first one and buy the all day ticket.

Thanks everyone, do I need the all day pass if we are just taking the ferry north and then walking back ? I suppose we could get the ferry from Riomaggiore to Portovenere when we have finished our walk ? Make sense ?

I would not get a day pass for just 1 day. They make the most economic sense to buy in longer day increments (4-6 days). There is no need to buy the ferry tickets online or in advance. You can just walk down to the harbor and select the boat time you want to go (same day). If you want to take the ferry after your walk, you can catch it from any of the towns, or just from Riomaggiore down. Dependent on how tired you are from walking! I like the ferries because of the coastal views and fresh ocean breezes (vs the train or walking).