Minimum connection time in JNB between DL and SA is 1:30. I assume this was booked on separate tickets? If so, you will need to bring a copy of your SA itinerary and confirmation number so that Delta can check the bags through.

Also keep in mind that if it is on a separate itinerary neither DL nor SA has any obligation to reaccommodate you if you miss the connection in JNB. Delta's obligation ends when they deliver you to JNB and SA's begins when you have checked in for the flight according to their respective cutoffs (assuming on different tickets/reservations).