David, temperature is indeed important and should be monitored as carefully as you can - and that includes the other chemicals and wash water, which ideally should all be at or pretty close to the developer temperature. Try to do the best you can - and as I think Bill pointed out earlier keeping the process to within a few degrees sounds harder than it actually is. Also, today's materials from Ilford, Kodak and Fuji are pretty forgiving, and even if you're off a little you'll probably get a pretty good negative. Printing controls give you a lot of lattitude. The notion you need a perfectly exposed and developed negative to make a fine print is false, and dangerous. Do the best you can, but realize many of the great prints you've ever seen by the finest photographers were made from imperfect negatives. This is why I highly recommend inexperienced darkroom practitioners begin with a good basic book, and/or the how-to publications from Ilford and Kodak. Web forums etc can be great for discussion and problem solving, but information overload (both good and bad information unfortunately) on any given topic can become confusing and make the entire process seem almost impossible to do well.
Originally Posted by David Goldstein