Athens is 6 hours behind Shenzhen
Best overlap: 2:00 PM to 6:00 PM in Shenzhen is 8:00 AM to 12:00 PM in Athens.
Your window to reach both cities is 2:00 PM to 6:00 PM in Shenzhen, which converts to 8:00 AM to 12:00 PM in Athens. With about 4 hours of overlap, there's comfortable room for a daily stand-up — 2:00 PM in Shenzhen / 8:00 AM in Athens works well. Note the seasonal wrinkle: when Athens is on daylight saving and Shenzhen isn't, the gap between them grows or shrinks by an hour.