Are you talking about the Island of Poros or is there somewhere else with the same name? If so, how are you going to make the last 500 metres over the sea from the mainland to the island when the water taxis will be locked up for the night and will not be operating until about 9 in the morning? Also, I would say that Poros was more like a 5 or 6 hour drive from Athens and not two. It's nigh on 2 hours to Corinth and you are travelling at least double that distance and more!
Personally, I would find a nice spot in the airport for a few hours for a rest or leave your luggage at the airport and go clubbing! You can always catch up on sleep the next night.