It is much shorter than from Cameron Pass. From trailhead to Lake Lillian was about 8 hours, but if I did it again, now that I know the rout, it would be a bit quicker.
I did the Lillian Glacier Route a couple days ago. At the time, McCartney was a last minute decision so we were sort of making it up as we went along without any prior research. When I got home I found your page and was very pleased that we chose the best and most direct way.
I think it is pretty close to the guidebook directions. From Lake Lillian you can sometimes see a bit of a trace from the old trail following almost the same route.