Houston is 10.5 hours behind Colombo

There is no standard 8-to-6 overlap. Someone joins early or late.

The 10.5-hour offset between Colombo and Houston means there's no point hunting for a 9-to-5 overlap — there isn't one. Expect compromise: someone in Colombo or Houston will need to take the call outside the usual 9-to-5, so share that load. Because Houston and Colombo don't both observe daylight saving, plan to re-check the overlap around March and November.