How Long in the Brooder?

I typically only leave them in till they're dry/mostly dry. Just make sure you don't lift the lid too often, or you'll lower humidity which can easily ruin the remaining eggs.
It's recommended that you lower the temp 5 degrees every week, starting with 90 (but personally I find that way too high ).

 

When it was 100+ degrees here, I didn't use a lamp at all, infact, I turned my AC on during the daytime for them.

Now that it's cooling off, I use a lamp mostly at night, and remove it during the daytime. Once they are 3ish weeks old, I turn it off completely.

Once they are 4-6 weeks old, they get booted out of the house with a shelter, as long as there's a group of them to huddle together and stay warm. But I live in texas, and it doesn't get below 60 at night, even when it's' raining or stormy out. By the time we get colder weather, they'll be all feathered up and big enough it's not an issue.

Once they are a week old or so, I'd start dropping the temp, see how they do with out the light for a few hours, are they huddled together, shivering/acting cold? what's the temp of the area you're keeping them in? If it's above 75-80, a group of them can likely be fine with out a light on 24/7

 

Young chicks need constant access to a heat source. However, the whole brooder does not need to be heated. Just the spot under the heat lamp should be warmed. The rest of the brooder should be at least 20 degrees cooler. Your brooder needs to be large enough to accomplish this.
Once they are mostly feathered, they no longer need heat.
I prefer using a heating pad instead of a heat lamp. The chicks get used to a normal day/night cycle, and they can better regulate their own temp.

 

The ones I get from the hatchery, go straight into the brood cage. No light, no heater unless overnight temperatures drop below 70, then they will get a space heater at night. I generally have batches of 25 chicks or more at a time though, so they keep each other warm. as long as you have at least 12 chicks and they are on full feed you don't have to coddle them. In fact too much coddling can make them weaker.

Yes every one is precious. No they aren't as fragile as you may think.

 

This is where region and time of year play a big part. It rarely gets over 70* during the day here, even in the middle of summer. Not everyone lives in such a warm climate.