delay of 18:06 flight from Hre to Jhb

Bought a ticket for my sister for a flight scheduled at 18:05 for flight for 22 July 2015 and was told by my sister that the flight has been delayed to 22:00 and am wondering if this is a coincidence last month a friend of mine went to Zim and on retuning back of Sunday 21 June 2015 the flight was delayed again to 22:00hrs. Why dont they reschedule for 8pm or 9pm but 10pm? Just thought i have to advise people that they should be prepared to book for an 18:00 flight and depart at 22:00 with Fly Africa! That's the additional cost to pay! Not so cheap now we must get ready to go to OR Tambo Airport around to pick her something we didn't plan to do around this time as we should have been back by now