Ideally, You ought to make it possible for three-5h of transit time in Johannesburg, so that you've sufficient time and energy to capture your connecting flight. Transiting in Johannesburg is rather straightforward; only Keep to the indications for ‘Worldwide Transit’. The flight from Johannesburg to Harare takes about 1h 30m. https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/