If you arrive at Athens Airport after 22:00 local time, you will NOT make it to KBL on the same day with public transport.
If you departure from Athens Airport before 9:00 am, you will NOT get to the airport in time with public transport on the same day. You have to travel to Athens on the day before your departure unless you find a private lift by car to the airport.
In both cases, please get in contact with our friends from the Athen’s Sangha. They will try to accommodate you for one night in the center or give you advice on where to stay in Athens.