Per my Storey's Guide to raising chicken's book (very helpful by the way), it says that you start out with 95 degrees and each week you reduce by 5 degrees until you're at room temperature. After that it's based on when the chicks feathers come in as to bringing out into the cold.
I hope you have a large area for them. The first time we got 25 chick (1993) we weren't prepared and ended up giving them the entire back porch. Them little buggers get big quick. I had my last batch in the hen house by day 45 with no problems, but I did leave a lamp on in the coop for another month. This batch will go in a little later so they are bigger and will have to be introduced to the current flock.
Here's a tip on the heat lamp for you. Always have an extra bulb! They don't last for nearly as many hours as they say on the box. It's always good to be prepared in case one burns out when you can't get to a store for a replacement.