If possible, you'll want to allow for 3-5h of transit time in Johannesburg, so that you've got sufficient time to capture your connecting flight. Transiting in Johannesburg is rather uncomplicated; only Stick to the indicators for ‘Intercontinental Transit’. The flight from Johannesburg to Harare can take about 1h 30m. Does https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/