keithwms, you make it sound quite difficult .
I have always used a "take it easy" mentality and still I always have good negs. But, I'm quite careful by nature.
A small deviation in temperature, like 1F, is not critical, but if the deviation for some reason is something like 5 or 10F, then it probably is the culprit.
You can practice with water in tank instead of developer and measure the actual temperature of the water in the beginning, middle and end of the processing time (3 min 15 sec).