Prague is 1 hour behind Helsinki
Best overlap: 9:00 AM to 6:00 PM in Helsinki is 8:00 AM to 5:00 PM in Prague.
Plan around 9:00 AM to 6:00 PM in Helsinki, which is 8:00 AM to 5:00 PM in Prague, 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.