Mexico City is 9 hours behind Athens
Best overlap: 5:00 PM to 6:00 PM in Athens is 8:00 AM to 9:00 AM in Mexico City.
The overlap falls at 5:00 PM to 6:00 PM in Athens, or 8:00 AM to 9:00 AM if you're in Mexico City. Because Mexico City is 9 hours behind Athens, the shared window is only about 1 hour. A fixed slot at 5:00 PM in Athens (8:00 AM in Mexico City) saves a lot of back-and-forth. The window above shifts seasonally: Athens keeps daylight saving while Mexico City ignores it.