Ideally, you need to let 3-5h of transit time in Johannesburg, so that you've got enough time for you to capture your connecting flight. Transiting in Johannesburg is quite easy; basically Keep to the indicators for ‘International Transit’. The flight from Johannesburg to Harare takes about 1h 30m. *Fares displayed https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/