It's 12 months, Selchie and as far back as I can remember it's been the same. Not sure what I can bring up in the way of a link showing this at short notice, but the general word on the street is always 12 months, at least these days it is. Thought the time limit for paying the Migrant Levy was 4 months, too, not 6 although I must admit to having heard it was 6 a short while back so that must have changed. Just how long ago did you apply? Perhaps you applied when I was just cutting my teeth on immigration and things were different then. If you did have 24 months I wonder if that still applies.
Sounds like you might have to move fast.
Edited to add: Just found
this. If you find R5.65 on page 69 under Residence visas, it states there that you have 12 months and it looks like it's from the original Immigration Act of 1987.