http://bushwalk.com/forum/viewtopic.php?f=3&t=1848This topic has a little info about the King William Range. The route follows a 4WD track for much of the way, which would be a lot easier than straight over the button grass in my opinon. Once you get to the end of the 4wd track, the climb gets steep on a cairned route with the occasional snow pole. I reckon it was about two hours to the top, and I was carrying an overnight pack so could potentially be quicker.
From the attached topic, it looks like mountain goats like Stu can do KW1, Milligans and Pitt in one day. It was certainly fantastic open walking on top of the range.
Enjoy.
Wello