Agree with ST2, 3 days is more like it. The KBC side is longer and more strenuous than what it may look, and the Cowl Fork side is steep, full of loose scree and boulders and fairly treacherous at times - nothing you can quickly descend safely.
I'd also like to establish a proper name for this route (the section between KBC and Cowl Fork campsite), since it doesnt seem to have one, and it goes by different names. "Cathkin gully" for me is too closely linked to Cathkin South Gully climbing route, "Cowl gully" could work, but its not the only gully around the Cowl, and "Cowl Fork" is just half of it. I think too that restricting it to the word "gully" is limiting, because in reality this route is a "pass" - maybe not the ones we are used to in the Berg, but still a proper one in the classic sense. Any suggestions here?