Completed Summit on August 4th. here are my suggestions
1) 9 pm to 2 am - Take nice rest in Hotel. Safe and rest is better.
2) 5 liters is good. But carry filter just in case. last filter stop near Trail camp 6 miles from Portal. 12000 feet.
(Just in case... is important...There might be unplanned delays. Someone gets altitude sickness and you have to give company. Thunderstorms... tiring etc.)
3) one spare pair of socks is safe. You cross 6-7 streams on proper logs, rocks. But just in case you slip. None of us needed it.
4)No snow on trail. No microspikes needed.
5)keep an eye on weather forecast
https://www.mountain-forecast.com/peaks/Mount-Whitney/forecasts/4418
Good luck, worth it.