Mumbai is 3.5 hours ahead of Johannesburg. Johannesburg uses SAST (UTC+2). Mumbai uses IST (UTC+5:30).
When it's 12:00 PM in Johannesburg, it's 3:30 PM in Mumbai.
Morning Jo'burg, afternoon Mumbai! 9:00 AM in Johannesburg is 12:30 PM in Mumbai - great overlap.
South Africa has a large Indian diaspora. Air India and other carriers operate direct flights between Mumbai and Johannesburg taking about 9 hours.