I have been searching through the posts and have found several responses that touch on my question but I could use a direct response from someone who knows. My family of four will be spending time on Santorini, Naxos, and a third island to be determined later. I think the best idea is to go to Santorini first (from Piraeus) on a night ferry so that we will take the longest leg of our travel when we can be sleeping and we will in effect gain a full day in Santorini. I've searched the sechedules from some of the linkes posted in this forum and came close with the www.gtp.gr link. It looked like there was a Hellenic Seaways ferry leaving at 22:00. But when I linked to their site to book, Hellenic shows no such departure. Does anyone have the solution or will I have to decide between waiting until we get to Athens and take our chances, or changing my desired itinerary? Thank you in advance for your help.

Another question while I've got your attention. Does anyone have any suggestions if we're trying to pick between La Perla Villas, Delfini, and Ether Studios while staying in Oia? Thanks again.

When are you travelling? Tomorrow, Hellenic Seaways' EXPRESS SANTORINI leaves Pireas at 2200 for Santorini. Greek ferry schedules are not fixed months in advance and firm schedules are available for only the next week or two.

So sorry to leave that essential date out of my original post. We plan to arrive in Athens (from Venice) on June 24 at 21:00. I'd prefer to take a night ferry that night but I doubt that's possible. My second choice is to do some sightseeing in Athens on the 25th (saving the bulk of our time in Athens for the back end of our trip) and take a late ferry out the night of 6/25. I see the ferry that you mention on 5/21 when I try their online booking at www.dolphins.gr. That schedule would be perfect, but when I tried to enter a departure date of June 25 I get the response "No departures for this specific itinerary." After some more experimentation, I see what you mean about them only loading several weeks into the future. The latest date in June that I could find the 22:00 boat was 6/15. Perhaps I can send them an email to ask if they can tell me if their 22:00 departures from Piraeus will likely continue through the end of June. Thanks for your response.

The number of sailings will increase before the peak season in July and August. Any service that is running now in May is pretty sure to be running in June, and it is possible there will be more services.
You didn't say how or where you're arriving in Athens, but if you arrive at 2100, catching a ferry from Pireas at 2200 could be difficult.

Basically you are arriving too late for any ferry from Piraeus. The first you will get is one of the 07:30 departures. Ferries change their schedules during June, but there is always plenty going to Santorini. The best up to date information will be from the ferry agent the day you arrive.