21 hours, including a stop for fuel, from Jo’burg to Atlanta. The stop was just long enough to take on fuel. We were not allowed off the aircraft.
I spent a lot of time walking up and down the aisle and doing calf raises.
You can go from the East Coast to JNB nonstop, but you can’t come back because the plane can’t take off with a full fuel load (elevation).
On my trip, we landed at 2am to refuel in Sal (Cape Verde), and the international transit “lounge” there was like a scene from Dante’s inferno.
SAA has been experimenting with various stops in West Africa for the JNB-USA refueling, but I don’t know that they’ve settled on a permanent solution.