Helsinki is 1 hour ahead of Hamburg
Best overlap: 8:00 AM to 5:00 PM in Hamburg is 9:00 AM to 6:00 PM in Helsinki.
Plan around 8:00 AM to 5:00 PM in Hamburg, which is 9:00 AM to 6:00 PM in Helsinki, to catch everyone during office hours. That's a roomy 9 hours of common time each day, so finding a slot that suits everyone is rarely a problem.