ChevyII, on hiking overnight: I just don't think you would be stopped in the night. If you are really intending on hiking through the night, I think I would get the overnight permit, so you are ok no matter where and when your permit might be checked. Whether you are carrying overnight gear shouldn't matter.
I am really wary, though, about your plans to hike through the night. Getting sleep before starting (in the early evening?) would be really difficult -- noise from cars and people...no way to sleep. Who can force themselves to sleep before a big trip, anyway? Thinking about it.... I think I would take warm clothing and a short foam pad (maybe a down "blanket" too), and consider napping part way up the trail (but that then becomes an overnight trip). I know for myself, it would be lots easier to hike up to Trail Camp, sleep 2 - 4 hours there, then get up at 1 AM and hike to the summit. That way, you could also catch a nap on the way down, too.
It could be really tough trying to hike in a sleep-deprived state. I think your enjoyment of the morning sunrise would be diminished for the same reason. Also, remember that your F.I.L may not be in the same super condition as you, so consider his abilities, too.
btw: I think Little Lakes Valley is an excellent place to day hike and acclimate.
