Portland is 11 hours behind Nairobi
There is no standard 8-to-6 overlap. Someone joins early or late.
Practically speaking, Nairobi and Portland never share office hours; 11 hours of separation keeps their days apart. To talk live, someone has to flex: an early start in Portland can catch the tail end of the day in Nairobi, or the other way round. The difference isn't constant year-round: Portland adjusts for daylight saving while Nairobi holds steady.