Ideally, it is best to let 3-5h of transit time in Johannesburg, so that you have ample time for you to catch your connecting flight. Transiting in Johannesburg is quite easy; simply Adhere to the signs for ‘Intercontinental Transit’. The flight from Johannesburg to Harare usually takes about 1h 30m. https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/