36"!! Is that just what you did or is that what you have to do?
24" + 12" extension = 36" (8-pins CPU power cable) is what I did in order to route the cable behind the motherboard panel. My case is HAF 932. The HAF 922 is very similar as far as cable routing is concerned.
If you want to route the cable behind the motherboard panel, you will have to get a total length of 36".