Well, I guess I wouldn't push it past mid September now that I think about. Labor Day is Sept 3 of next year, so if I started the trip at the end of that week, I'd go to Yosemite first, and then some other Sierra locales, and then I'd probably be hitting Whitney right around the middle of the month. So I guess I need to know if it is usually very icy during mid September up there near the end of the MR above the notch. That's the part of the climb that I am most concerned about.
I assumed that Yosemite would still be mobbed up until Labor Day, but maybe not because school does start back earlier as you say. But I'd still like to avoid Labor Day weekend, so it may be best to go afterwards.
I haven't thought much about where I'd go in Yosemite I wanted to check out all the main areas as I'd have a couple of days or longer if I wanted.
I was thinking I'd do the Clouds Rest hike, but I'd love an even better hike to prepare for Whitney, so I'll have to check into Mt. Dana and do some research on that one.
As far as high elevation "prep" hikes, I was also considering Mount Morgan as "wingding" recently posted her photos from that hike and it looked great. I think it is 13K+ as well. But I can't see doing more than a two or three long hikes before Whitney or I'll be too worn out by the time I get to it at the end of my trip. Although I hope to train hard for a few months beforehand, so maybe I'll be able to handle it better than I think.
There are probably so many amazing hikes in the Sierra and it is going to be tough to narrow it down to two or three. I'd like to find some where the campgrounds are at very high elevations, so that will help with acclimatization as well.
But I don't want to go off on a tangent and I hope I can get some more opinions on the conditions on the MR during mid September.