Hi there BCS112.
coming from Joburg myself and worked at the airport for years I can tell u that all European carriers sit at Joburg Intl the whole day. some of them are 2 x air France, 2 x BA, Iberia, VS, Swiss and Luthansa. The reason they stay at the joburg is that they will not make it back to europe in time for connecting pax and airport curfues. Lets say they arrive between 8 to 10 in the moring and then 2 hours later have to depart, around 12, its still a 11 flight back to europe and all the pax will miss their connecting flight, its also kinda strange to arrive at an airport round about 22H-23H.
Once the aircraft arrive at joburg they are towed to the remote stand "Delta" or they even arrive their. Then the cleaners have the whole day to clean and dress the airport. Some of the planes gets washed and polished their asits so cheap. They also fuel the aircraft to Minimum sector fuel. If u ever seen Joburg airport between 19H to 21H u will understand that getting a bowser to fuel u for 1 hour is almost impossible, so thet only top up once the final ZFW comes. hope this helps. cheers