Hi Mike,
Good luck on your trip. Yes, you should read up a bit if you are not too familiar with the area/climb.
Not sure what your climbing/hiking experience is, but you can read my recent trip report from Oct 9 for conditions then and see some photos along the trail. Also, the aforementioned advice from Kurt is valuable as well, especially for the season. Are you accustomed to being at elevation?
If you're friends are well conditioned, previously acclimatized and/or live at higher elevation and have the right gear and water, they could indeed just "walk to the summit"...albeit in a LONG walk...However...
If not, they are in for a bit of a surprise and could encounter conditions that are outright dangerous on the 21st. I assume you're referring to a dayhike? Plan on at least 12 hours for a roundtrip dayhike - a few more if you are not travelling light, stopping for photos and very fit. Most people doing it in a day leave the trailhead at 2AM - 4AM.
I would recommend picking up one or more of the books written on climbing Whitney (like the one by the owners of this store actually, which is quite good). Read the other posts on this site too.
In short, you need to be in good shape, have proper gear (warm clothing, traction devices for your boots, walking poles help, etc and carry enough water..). Unless you live in a place like Estes Park Colorado which is 7000-8000ft, you will need to be acclimatized to the elevation for at least a few days, otherwise you a courting trouble and are in for a very uncomfortable hike and risk altitude-related problems. Among the most important, you need to be psychologically prepared for the long climb.
You should also be aware of the weather and how it can impact trail conditions. Have a backup plan if a storm moves in and makes the climb too risky. The 21st may be a beautiful sunny day with no wind or could be below freezing in winter conditions with ice and snow most of the way up.
Also, know that in the first few miles of the trail (and last few returning) you will be hiking though prime bear habitat and need to aware of the possibility of encountering a bear. While these are black bears, not grizzlies, they still should be treated with respect. It is likely they will be more scared of you than you are of them, but during this time of year, they are in hyperphagia, searching for food anywhere they can (packs, tents, cars etc...) prior to hibernation and may become aggressive if they consider you a competitor for a food source. Be bear aware...if you are not concerned for your own safety, think of the bear; a bear that gets into human provided food will often later wind up dead from habituation or other encounter...a fed bear is a dead bear.
For your trip, where you say you are "planning to summit"...I would change the perspective and say that you are planning to hike and will summit if conditions allow. Weather has a nasty way of altering even the best laid plans. Managing your expectations is also important and be careful going up what you fear you may not be able to get down. Never be ashamed of turning back to climb another day, even if your friends are pushing on in questionable conditions.
Good luck.
Rob
