Ottawa is 7 hours behind Johannesburg
Best overlap: 3:00 PM to 6:00 PM in Johannesburg is 8:00 AM to 11:00 AM in Ottawa.
Johannesburg and Ottawa overlap from 3:00 PM to 6:00 PM (Johannesburg) to the equivalent 8:00 AM to 11:00 AM in Ottawa — that's your meeting window. Roughly 3 hours of shared hours means scheduling takes a little care — 3:00 PM in Johannesburg / 8:00 AM in Ottawa is a safe default. Note the seasonal wrinkle: when Ottawa is on daylight saving and Johannesburg isn't, the gap between them grows or shrinks by an hour.