If Possible, you need to allow 3-5h of transit time in Johannesburg, so you have sufficient time to catch your connecting flight. Transiting in Johannesburg is very straightforward; just Adhere to the indications for ‘Intercontinental Transit’. The flight from Johannesburg to Harare can take about 1h 30m. KAYAK’s flight Price https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/