If possible, you'll want to allow 3-5h of transit time in Johannesburg, so that you've got enough time to catch your connecting flight. Transiting in Johannesburg is rather easy; simply just Keep to the symptoms for ‘International Transit’. The flight from Johannesburg to Harare usually takes about 1h 30m. Delayed https://www.theluxurybooking.co.uk/flights-to-zimbabwe-from-london/