Shenzhen is 6 hours ahead of Helsinki
Best overlap: 8:00 AM to 12:00 PM in Helsinki is 2:00 PM to 6:00 PM in Shenzhen.
Your window to reach both cities is 8:00 AM to 12:00 PM in Helsinki, which converts to 2:00 PM to 6:00 PM in Shenzhen. The overlap sits at about 4 hours; aim for the heart of it so the call isn't too early for one team or too late for the other. One seasonal catch: Helsinki springs forward and falls back, but Shenzhen doesn't, so the gap changes by an hour for several months of the year.