Pireaus Port to Intl Airport

Yikes.

First off, Greek time is a little soft. You may or may not arrive at 3:30 pm.
Then you’ll have to disembark and get a car. Add 10-15 minutes. That brings you to 3:45 pm.

It will take you 45 minutes to drive to the airport, and that’s if there is no traffic. You are now at 4:30 pm.

Your boarding time is 30 minutes before your flight. That means boarding time is 5:00 pm.
That gives you 30 minutes to check any bags (if you are checking bags) and also get through security.

Good luck, you’re going to need every bit of it.

Personally, I would arrive at a strange airport 2 hours before a domestic flight. That would be 3:30 pm.

That is a squeaker.

There are many options, but a taxi looks the fastest. Rome2rio gives these comparisons along with a list of Taxi services. Click on the taxi option. Can't imagine why you'd rent a car for the transfer, but maybe I missed something.

It will be tight but a taxi (around €50) will be fastest as you won't have to look around for one. They'll be easy to flag down wherever you are. It will take just over an hour to get to the airport, so if you've already printed out your boarding passes (up to 48 hours in advance) for the flight to Kos you should be able to make it. Good luck!

You have a degree of optimism that eludes me.

You seem to be one small hiccup from disaster. Change to 'Plan B" now or at least have one ready in case things do not go smoothly.

I agree with everybody else that this is just too tight. If you decide to risk it though you might want to book a driver with Welcome Pickups. We’ve used them a couple of times in Athens recently and found them reliable

https://www.welcomepickups.com/athens/

They’ll give you an online quote.

Alan

I'll have about 6hrs to tour the city of Athens

Is the "~6 hrs" the time between your flight's scheduled arrival and the departure time of your outbound boat?.

If so, you may want to find an restaurant near the port and enjoy a meal and recover from the flight and jet lag, before your boat trip out to where ever.

From the time your plane parks until you arrive in central Athens is unlikely to be less than 2 hours. Then factor your time to get to Pireaus (port) and dealing with your luggage and you have very little time to 'tour' Athens.

Another question for Joe:
So I'll refine my agenda for this leg of my trip:
I arrive in athens about 9:40am and thinking about 2 hrs to collect my luggage and go thru customs, so that takes me to 11:30 am.
and I meet my transfer group at Athens Airport at 6:30 pm. So do I nix a tour and just relax close to airport?? Thanks for you input!!

The issue with booking a tour is having no way to know for certain when you will arrive in core of Athens. Is the plane on time; how long is the line at passport control etc.

If you have to meet your group at the airport, you need to plan for an hour each way to/from the city.

Best thought I have is to leave luggage in storage at the airport, take the Metro to town, wander around the Acropolis and find a restaurant with a view and have a meal. Trying to set up a 'tour' looks unfeasible, with your time parameters and uncertainty of your timing.

Short answer: No, 2 hours is not enough time from the ferry terminal to the airport, even in an ideal world.

I agree with stephb. No one has mentioned the heavy traffic you'll encounter after 3:30 that will slow you down even more.