Moscow is 2 hours ahead of Hamburg
Best overlap: 8:00 AM to 4:00 PM in Hamburg is 10:00 AM to 6:00 PM in Moscow.
Your window to reach both cities is 8:00 AM to 4:00 PM in Hamburg, which converts to 10:00 AM to 6:00 PM in Moscow. 8 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. Note the seasonal wrinkle: when Hamburg is on daylight saving and Moscow isn't, the gap between them grows or shrinks by an hour.