Hiking in the dark can be a beautiful experience or a disaster. You've received good advice from others, but let me tell you some of the benefits from my perspective.
After midnight, fewer mosquitoes. (I know I'll got differing opinions on this...)
You are forced to walk much more slowing, thereby enabling you to more fully enjoy the experience. Zen, anyone?
Cooler temperatures.
Fewer people on the trail; just the brave and/or foolish. More solitude, if you like that; fewer hello's and hi's to which to respond, and not many anti-social-thru-hikers, running to keep on their tight schedules.
More animals are around that tend to hide from people during the daylight hours...for instance:
Deer tend to browse at night during the Summer months; you might see two glowing yellow eyes about level with your face...don't worry...it's not a tall mountain lion...it's Bambi's clan having a nice feed in the nearby meadow.
At lower elevations, Mr. and Mrs. Racoon and family will be up an about; they scamper up into trees on the approach of humans.
Snakes: Nada; too cold...they've gone underground to stay warm.
Mountain lions and Bobcats: You'd be lucky to see one..especially the one watching you...eeek.
Rabbits and their hunter, the Coyote. If you camp on snow, you might see tracks of both near your tent in the morning.
Their is one creature you probably won't see at night in the mountains: most rangers go to bed after dark. So...if you don't have a wilderness use permit...hike at night! (Sorry, George...)
