Here's a little tip. The permits for Glacier Point are among the more popular in the park, and they sometimes go fast. (admittedly, if you are staying overnight in the park, you can usually get one by standing in line early...)
But Mono Meadows, which is nearby and actually CLOSER to Illilouette Canyon, almost never fills up. The shuttle stops there as well--it's about five miles before Glacier Point.
If it were me, I would get a Mono Meadows permit, take the shuttle there, and then hike down through Illilouette Canyon through Nevada Falls, and down into the Valley.