Helsinki is 5 hours behind Hong Kong

Best overlap: 1:00 PM to 6:00 PM in Hong Kong is 8:00 AM to 1:00 PM in Helsinki.

For the smoothest call, aim inside 1:00 PM to 6:00 PM in Hong Kong, i.e. 8:00 AM to 1:00 PM in Helsinki. A 5-hour overlap gives you a workable daily window; aim for earlier in it to avoid clipping the end of someone's day. For part of the year the maths changes: Helsinki observes daylight saving, Hong Kong does not, shifting the overlap by an hour.