Hanoi is 12 hours ahead of Houston

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

Set against a 12-hour difference, Houston and Hanoi run their workdays on completely separate schedules. Block a single recurring off-hours slot that both teams agree on, rather than negotiating a new awkward time every week. For part of the year the maths changes: Houston observes daylight saving, Hanoi does not, shifting the overlap by an hour.