Preferably, You ought to make it possible for three-5h of transit time in Johannesburg, so you have ample time for you to catch your connecting flight. Transiting in Johannesburg is rather effortless; simply just follow the signs for ‘Worldwide Transit’. The flight from Johannesburg to Harare normally takes about 1h https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/