Best overlap: 10:30 AM to 6:30 PM in Shenzhen is 8:00 AM to 4:00 PM in Kolkata.
10:30 AM to 6:30 PM in Shenzhen is when Kolkata is also working, at 8:00 AM to 4:00 PM their time. Even with Kolkata behind by 2.5 hours, your workdays overlap by a comfortable 8 hours — plenty of flexibility for both sides.
A complete guide to time zones in 2025, from UTC and GMT differences to Daylight Saving Time changes, IANA database rules, abbreviation pitfalls, and developer best practices for handling global time. -