Shenzhen is 2.5 hours ahead of Colombo
Best overlap: 8:00 AM to 4:00 PM in Colombo is 10:30 AM to 6:30 PM in Shenzhen.
The overlap falls at 8:00 AM to 4:00 PM in Colombo, or 10:30 AM to 6:30 PM if you're in Shenzhen. Even with Shenzhen ahead by 2.5 hours, your workdays overlap by a comfortable 8 hours — plenty of flexibility for both sides.