Ideally, you need to allow 3-5h of transit time in Johannesburg, so that you have enough time for you to capture your connecting flight. Transiting in Johannesburg is rather quick; simply just Stick to the signs for ‘Global Transit’. The flight from Johannesburg to Harare usually takes about 1h 30m. https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/