Hamburg is 1 hour behind Johannesburg
Best overlap: 9:00 AM to 6:00 PM in Johannesburg is 8:00 AM to 5:00 PM in Hamburg.
Both teams are at their desks between 9:00 AM to 6:00 PM in Johannesburg and 8:00 AM to 5:00 PM in Hamburg. 9 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. The difference isn't constant year-round: Hamburg adjusts for daylight saving while Johannesburg holds steady.