The longest day hike I did for my 2nd kick at day hike can was 16-miles, +4,600'. I felt comfortable the whole day. I was tired at the end but not totally spent, like I was two years earlier.
Experience is the key to success for the Whitney noob. This is includes long distance hikes, hiking at night, hiking to 14,000', learning about the trail and learning about what works for them. Many start too late, do too little and have to came back a 2nd and 3rd time to succeed.
