Nairobi is 11 hours ahead of Portland
There is no standard 8-to-6 overlap. Someone joins early or late.
Given Nairobi is 11 hours ahead of Portland, the realistic answer is that there's no convenient shared slot during normal business hours. Catch the edges of the day: the last hour for Nairobi or the first hour for Portland is usually the least painful option. Just remember Portland changes its clocks for daylight saving and Nairobi doesn't, so confirm the overlap whenever the seasons turn.