Chennai is 2.5 hours ahead of Helsinki
Best overlap: 8:30 AM to 3:30 PM in Helsinki is 11:00 AM to 6:00 PM in Chennai.
If you set up a recurring sync, 8:30 AM to 3:30 PM in Helsinki (11:00 AM to 6:00 PM in Chennai) is the natural home for it. With 7 hours of daily overlap, these two cities are an easy pairing; almost any reasonable hour works. Remember that Helsinki shifts for daylight saving and Chennai doesn't, so recalculate the overlap after each clock change.