Preferably, it is best to make it possible for 3-5h of transit time in Johannesburg, so that you have sufficient time to capture your connecting flight. Transiting in Johannesburg is quite simple; just follow the symptoms for ‘Worldwide Transit’. The flight from Johannesburg to Harare usually takes about 1h 30m. https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/