Johannesburg is 2 hours ahead of Reykjavik
Best overlap: 8:00 AM to 4:00 PM in Reykjavik is 10:00 AM to 6:00 PM in Johannesburg.
Both teams are at their desks between 8:00 AM to 4:00 PM in Reykjavik and 10:00 AM to 6:00 PM in Johannesburg. 8 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved.