Hamburg is 1 hour behind Athens
Best overlap: 9:00 AM to 6:00 PM in Athens is 8:00 AM to 5:00 PM in Hamburg.
Schedule calls for 9:00 AM to 6:00 PM in Athens — your colleagues in Hamburg will be online from 8:00 AM to 5:00 PM. With 9 hours of daily overlap, these two cities are an easy pairing; almost any reasonable hour works.