Kathmandu is 3.75 hours ahead of Athens
Best overlap: 8:00 AM to 3:00 PM in Athens is 11:45 AM to 6:45 PM in Kathmandu.
Athens and Kathmandu overlap from 8:00 AM to 3:00 PM (Athens) to the equivalent 11:45 AM to 6:45 PM in Kathmandu — that's your meeting window. 7 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. Bear in mind Athens shifts for daylight saving while Kathmandu stays fixed — recheck these hours after each clock change.