The rule is you can't leave the trailhead until 12:01 AM on the day of your permit...that's the rule. What follows is the reality...no ranger is going to be around at 10 PM the night before. If it were me, I would not worry about being illegal, I'd go up the trail.
Where I might find fault with your plan is your pack weight, 6.5# of water and 3# of pack leave little room for this and that plus warmies...and you might need a pot full of warmies.
I have done two trips in mid to late September both put me on the summit prior to sunrise...which means my wake up call at Tarns above Guitar Lake was ~12:30 AM. Both times I ended up with a lot of damp clothing when I reached Mt. Whitney. The first time up the temperatures were in the single digits with 30 MPH winds; last year it was just below freezing and calm...as an aside with single digits and wind during one of August trips. Sometimes these trips have to planned like its winter...extra gloves, a balaclava and a heavier insulation layer than you thought about bringing.
