Three and a half hours, and most of the day shared
South Africa runs on UTC+2 and India on UTC+5:30, and neither changes its clocks, so Johannesburg is three and a half hours behind IST in every month of the year. 08:00 in Johannesburg is 11:30 in India; 17:00 is 20:30.
That leaves a wide overlap. An Indian office open from 09:30 to 18:30 IST covers 06:00 to 15:00 in Johannesburg, so a distributor's morning questions arrive in the Indian lunch hour and can be answered the same afternoon. Only the last two hours of the Johannesburg working day fall in the Indian evening.
Schedule broadcasts in SAST, though, not IST: a campaign set for 10:00 by an Indian habit reaches Johannesburg at 06:30. And keep InfiQ's own support hours in mind: its team works in English and Hindi, on India time.