No doubt about it, this is a tough hike. You have to hike over both Kearsarge Pass and Glen Pass to reach Rae Lakes. Since it's October, I was worried if I would have enough daylight before I returned back to the trailhead. So I didn't quite reach Rae Lakes. But I found a nice boulder to eat my lunch that overlooked Rae Lakes. (And I took some time to think about hiking BACK over those passes to reach my car. hee hee) You might want to just hike to Glen Pass, take in the awesome views and then return to Onion Valley. The scenery is spectacular everywhere, especially the view of the Kearsarge Pinnacles at the top of Kearsarge Pass.