NY? The database server MUST be screwed up, or the queries. I'm in Indiana??? Ok...(them Yonkers are always screwing with us Hoosiers... ) Anyways, Time & Temp:
Jill, It really depends on what process you are working on. If it's E-6, I'd say that time and temperature is somewhat critical. Why? Because the film IS the final product. No post-processing correction, etc. For C-41, time, temp, hell, even chemical life isn't as critical (I just got done developing 10 rolls of C-41 with chemical I mixed over 6 weeks ago from a C-41 kit made in 1992) and guess what? These negs print with the same tonality, density, and color filtration as the ones I processed with fresh chemical. Hmmm.
With C-41 (like B&W), you can have a few degrees + or -, or up to 15 seconds off either way. You can correct for any "oddities" in printing. The primary key is to be consistent. If you start the timer after pouring in the chemicals, always do the same, if you always start pouring after the timer hits 0:00, always do it.
The best thing to control temperature is to use a Jobo (used CPE-2's w/ lift go for about $150.00 these days) or get a nice Autolab. The three bath, room temperature kits are ok, but the don't always produce the best or most consistent results. I used one in a hotel room on vacation and the negs weren't bad, but when I tried printing the negs once I got home, there were about 5-10 C or 5-10 M variations between films.
For E-6, I always use the 6 bath. It lasts longer, produces more contrast, and is definitely more consistent. If you use an temperature controlled processor, the best starting temperature is 101-101.8F on the water bath. This allows for temperature changes, removals and lid openings, etc.
For RA-4 and P3000/30, I use a modified Ilford Cibachrome CAP-40 processor. Guess what? You "not supposed to" run RA-4 at 83F, but 83F @ 2 minutes (which is what the process does and only does) works great. I've done a ton of production AND competition prints off this machine and I paid...uh, nothing, for the machine.
Now, as far as testing go, I don't read charts, I hate other peoples tests (I'm a firm scientist/scientific believer that "I don't believe until *I* do/see") and I keep deeply detailed notes. So, when I test, I use real-world tests (not "ideal condition" testing). Again, the only point to really maintain is to be consistent throughout the testing process.
What it really boils down to is: the notes about consistency that you read in all the chem packaging is to make people paranoid (X-files?) but, the paranoia keeps people on their toes and makes beginners with that chem pay attention.
Also, the numbers for time and temp you read are the numbers that were established by the manufacturer in their testing. So, they are more like "suggested, starting point" type numbers. If there were no "starting" numbers, there'd be a lot of people pissed off because they'd waste a whole 100 pack of paper trying to establish their first print!
Oh, and I usually exceed the recommended roll count per batch of chemicals too. (usually is 5-6 rolls of 120 ISO400 per 500ml, I do about 10 rolls) and never noticed a problem. The first roll printed at the same color settings as the last roll. They were all shot in studio without the lighting or camera settings changing and on the same stock. Hmmm. Again, manufacturer's don't want to post high numbers like 10 rolls and then get a flood of calls from people who screwed up their 10th roll because of improper mixing (like using those inaccurate-as-hell plastic "beakers" and "graduates" and those people who don't understand the concept in chemistry of "use the smallest measuring device possible for the desired quantity". You know, the people that try to measure 10ml in a 500ml beaker...)
The MOST sensitve & destructive thing to do to your C-41 & RA-4 chemistry is to drip a drop (yes, 1 drop) of blix or bleach into dev! This can be common with some of the Jobo boxes because of the close proximity of the measuring tubes. A lift cures this problem, but some people insist on doing it without a lift and when careless, it'll happen.