Athens is 2 hours ahead of Reykjavik
Best overlap: 8:00 AM to 4:00 PM in Reykjavik is 10:00 AM to 6:00 PM in Athens.
Schedule calls for 8:00 AM to 4:00 PM in Reykjavik — your colleagues in Athens will be online from 10:00 AM to 6:00 PM. Despite the 2-hour difference, an 8-hour overlap keeps things simple and gives both teams breathing room. Remember that Athens shifts for daylight saving and Reykjavik doesn't, so recalculate the overlap after each clock change.