If Possible, it is best to let three-5h of transit time in Johannesburg, so that you have ample time for you to capture your connecting flight. Transiting in Johannesburg is rather easy; only Stick to the indications for ‘Global Transit’. The flight from Johannesburg to Harare normally takes about 1h https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/