Hanoi is 14 hours ahead of San Diego

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

Practically speaking, San Diego and Hanoi never share office hours; 14 hours of separation keeps their days apart. To talk live, someone has to flex: an early start in San Diego can catch the tail end of the day in Hanoi, or the other way round. Note the seasonal wrinkle: when San Diego is on daylight saving and Hanoi isn't, the gap between them grows or shrinks by an hour.