The #1 info above is incorrect. Goose is referring to an overnight hike -- that requires both the North Fork and the Exit permits. But for a DAY hike, the permit states Day Use All Routes.

If you have "memorized" the route that is good. But if you start early, it would be smart to get to Whitney Portal by early afternoon the day before, and scout out the Ebersbacher Ledges. You shouldn't try them in the dark the first time. I hope you have checked these links.

You don't eat as much as you might think, as your appetite diminishes as you go up, due to the altitude. Eat a big breakfast, either before starting, or at least by Lower Boy Scout Lake. Snack a bunch every hour on your way up-- like a granola bar. Drink lots of water-- a pint an hour is a good estimate.

I used to run -- 10-12 miles/week, 7:00-7:30 pace. If you're in that kind of shape, 12 hours should be good -- as long as you stay on-route.

Water: I dip and drink every time I go, never had any problems. Trail camp pond: get the water from the inlet.

Yosemite: I hope you have a pass to get into Yosemite. No pass, no entry. You must enter on the day stated on the pass, but then you're good to come and go for 7 days.