allowing time for customs when flying to Athens

Customs is 30 seconds at most. However, it is immigration -- passport control --- that can take time. There is no immigration in Canada or Turkey if it is just a connection.

Connection time at Athens airport.2 hours is sufficient.
This is what you can expect.
1) go to passport control.
2) Pick up your bags
3) Pass through the exit door. The door has a sign that says Nothing to Declare. That is customs. You are now in public area of arrivals level.
4) go up to the next level, stairs elevator or escalator.
5) I presume you will have already printed your boarding pass. They allow you to do that 48 hours before your flight. So all you have to do is drop off your luggage. You can go to the airline desk or as I recall there is a machine where you can print your own luggage tags.
6) right near that luggage tag machine you will see the bag drop off conveyor, drop your bags.
7) go to security. Athens airport has the most efficient security check process I have ever experienced.
8) head to your gate. You will likely have time for your first Mythos on the way.

Thank you. This was very helpful!

Yup 3.5 hours is plenty. You should have enough time to get through passport control, get something to eat, have a coffee, and relax a bit.

To clarify, when we connected in Toronto a few years ago, we did have to go through a special expedited passport control in Toronto for transiting passengers. Is that not still the case?

Yes if the OP chooses to connect in Montreal from the US they will have to go through passport control.

thank you for the clarification. We just bought tickets and will be going through Frankfurt.. Outbound we'll have a 5 hour layover and on the return 3.5 hour layover. I appreciate all the information. I've been in the Frankfurt airport and remember it is huge! It sounds like we should be ok..

You will have to go through passport control in Frankfurt. You will be cleared for all of the EU so when you arrive in Athens you just pick up your bags and walk out of the arrivals level and away you go.

As I recall we had several trips through Frankfurt all with 2 hour layovers and never had a problem making the connections there.

We just got back yesterday from 2 weeks in Greece and at least 3 ½ hours in your EU layover should be good (outside the June-Aug peak travel period). I don’t know about Germany, but I hadn’t expected the passport control delay in Amsterdam (outbound) where we had 3-hr layover. At least AMS had a line for those with connecting flights within than an hour. Nevertheless, still stressful not knowing how quickly lines would move; we made it in the nick of time.
However, inbound to US was much more stressful, connecting through Paris (CDG). CDG was less efficient and didn’t have the extra line; lines moved MUCH slower. No time to get food or go to restroom. We didn’t think we’d make it. Only when our flight announced boarding did CDG officials pull 50 of us through, by-passing passport control and getting us on the shuttle to board our plane.

There was no passport control in Athens when connecting to flights to Greek islands.
I can only imagine worse during peak-time travel.

You will have to go through passport control in Frankfurt. You will be cleared for all of the EU

Not true. When you go through passport control in Frankfurt you will be cleared for Schengen. Not all of the EU.

There is a difference between EU and Schengen. Some EU countries are not in Schengen (Bulgaria, Romania, Ireland and Cyprus) and some Schengen countries are not in the EU. (Switzerland, Liechtenstein, Norway, Iceland.)

I misspoke, Indeed one passport control at a Schengen country gives you access to the whole region. Thanks for the clarification.

Has anyone used either of the lounges in the Athens airport, domestic terminal? Goldair and Skyserv.

To P -- to sadder-but-wiser N. Americans, we all know that CHas De G. is the Transfer Airport from Hxll, to be avoided if at all possible -- terrible layout, unhelpful staff, looong security lines/passport llnes ... The last time I was forced to use it, I scheduled a full 3 hours for the connection and it was still Anxietyville. If your airline assures you that you can make a 90-minute connection... don't believe it.

I tried to use the lounge for Aegean but it was full and I was sent to one nearby. Nothing to write home about. Sorry, I don't remember the name.