Johannesburg is 7 hours ahead of Ottawa
Best overlap: 8:00 AM to 11:00 AM in Ottawa is 3:00 PM to 6:00 PM in Johannesburg.
The hours that work for both Ottawa and Johannesburg are 8:00 AM to 11:00 AM (Ottawa) and 3:00 PM to 6:00 PM (Johannesburg). The shared window is roughly 3 hours; treat its midpoint as the default and you'll keep both teams happy. Note the seasonal wrinkle: when Ottawa is on daylight saving and Johannesburg isn't, the gap between them grows or shrinks by an hour.