Why I wanted to know how long it would take. As a first timer (July 2) it was important for me to respect the mountain.
I knew it would be a long time 12+ hours.
I wanted to experience the trail without camping.
I wanted to pack the right amount of food and clothing.
I wanted to take the correct equipment.
I wanted to be emotionally and physically prepared, perhaps overprepared.
I wanted to succeed.
I wanted to enjoy it.
Thus I needed to know how long it took the average person, the faster person, the experienced hiker, the younger hiker, the older hiker, the sightseeing hiker, and so on. With that knowledge I could estimate how long it would take me and how long I could take without overextending my planning.
Within those bounds I had a nice experience.
That's why this first time Whitney day hiker also asked the question, "How long does it take? When should I, or can I start."