Just to add to the advice you have received, here is the process you will go through after you land in Athens.
Two hours for a connection in Athens airport is fine.
Here is what you can expect when you arrive.
1)go to passport control. This might take a few minutes. Your passport will be checked and stamped. The longest time we have experienced was 30 minutes when 4 transatlantic flights all arrived at the same time.
2)Pick up your bags
3)Pass through the exit door. That door has a sign that says Nothing to Declare. That was customs. You are now in public area of arrivals level.
4) go up to the next level, stairs elevator or escalator.
5) Aegean and Sky Express both allow you to print your boarding pass 48 hours before your flight. So, all you have to do is drop off your luggage. You can go to the Aegean or Sky Express kiosk 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 an exceptionally efficient security check process.
8) head to your gate. You will likely have time for your first Mythos Greek beer on the way.
Have a great time