Johannesburg is 11 hours ahead of Anchorage
There is no standard 8-to-6 overlap. Someone joins early or late.
Given Johannesburg is 11 hours ahead of Anchorage, 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 Johannesburg or the first hour for Anchorage is usually the least painful option. Watch the DST gap — when Anchorage changes its clocks and Johannesburg stays the same, this window slides by an hour.