Ideally, It is best to let three-5h of transit time in Johannesburg, so you have sufficient time for you to catch your connecting flight. Transiting in Johannesburg is quite effortless; simply just Stick to the indicators for ‘Worldwide Transit’. The flight from Johannesburg to Harare normally takes about 1h 30m. https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/