Preferably, you ought to make it possible for 3-5h of transit time in Johannesburg, so that you have enough the perfect time to capture your connecting flight. Transiting in Johannesburg is quite simple; simply follow the indicators for ‘International Transit’. The flight from Johannesburg to Harare usually takes about 1h https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/