Well, you know how steep Mount Whitney is. The trail gains a little over 6000 feet in 11 miles. Just for round numbers, think of that as 550 feet per mile.
The distance is one factor, and the elevation gain is another factor. The third factor surprises some people. That is that this 6000 feet of elevation gain _starts_ above 8000 feet. By the time you get above 14,000 feet, the air is getting pretty thin. If you are not adapted to it, it can really knock a hole in your pace.
I won't claim to be a speed demon, but I went up one time in 4 hours 15 minutes... and I was the slow guy.
You are best off if you start at a pace that you can maintain without major stops. There will be water obstacles that will slow you down from there.
By the time that I got a few years past my prime speed, I started earlier and earlier, so 3 a.m. is not out of the question. Some people start at 12:01 a.m. while the air is cool.
