If you want to camp in LYV the night before, then your trip becomes an overnight backpack with Half Dome tacked on. It is NOT part of the Half Dome day hike permit lottery. I think you can apply for that permit 6 months
(168 days) in advance using the Yosemite N.P. wilderness application and FAX.
I did that trip in Sept, 2015, and what I did was get a walk-in wilderness permit. They open at 8 AM, but don't do the Next Day LYV permits until 11. I got there and waited in line a little after 7 AM. There wasn't a high demand for the permit I wanted, and a few were available to start same-day (Friday). I then drove back home 2 hours, and returned the next day to start the hike with my daughter -- she was in school on the Friday I got the permit. They just don't make getting permits very easy.
