Whitney is the highest mountain in the continental USA.
Fedak linked to an amazing trip report.
By Rick Kent:
I started at midnight. For the first trip I decided to go up the Mountaineers Route. Despite going from Portal to summit (and much of the way back) in the dark I made good time. It helps that I know the route well. I reached the summit at 3:43am (3 hrs 40 mins from the Portal). I was alone on the summit and the hut was empty. I returned to the Portal a little after sunrise at 6:54am for a total roundtrip time of 6 hrs 51 mins.
This quick time had me briefly wondering whether a 3rd summit would be possible. That dillusion was thoroughly dispelled on my 2nd trip up. For the 2nd trip I decided to go for the Main Trail. I took a half hour break before starting. As much as I knew I needed to eat I couldn’t manage to get much down. I started up the Main Trail at 7:22am.
As I closed in on Trail Camp I began to slow noticeably. Both the MT and MR are hard on the calves (too many steps). Going up the switchbacks my speed slowed further. I past a few other hikers but only just barely. By the time I reached Trail Crest my calves were done. From Trail Crest to summit was agonizingly slow and my calves kept wanting to cramp up. For some reason I kept thinking about my first time up Whitney almost exactly 7 years ago. I reached the summit for the 2nd time at 1:11pm. I was thoroughly depleted. Time from Portal to summit was a less than stellar 5 hrs 49 mins. Roundtrip time was 9 hrs 33 mins.
I regained strength on the way down. I did some running but for the most part just took a fast pace. My priority now was to get down in time for a burger at the Portal. I knew this would probably be my last Portal burger for the year so I was well motivated. I reached the the Portal at 4:53pm. …
Although the 2nd summit was a bit harder than I expected both trips together took less than 17 hours combined. This marked my 28th and 29th Whitney summits.
besthike.com 
Good story about daily hiking.