Actually, that is how I worked-out annealing my .30 Herett cases. I used some old range pick-up .30-30 cases (that I did not want to chance shooting) as guinea pigs. I chuck a Lee case trimmer holder in my electric drill and hold the case neck in a set position in a torch flame, with the drill spinning the case to get even heat distribution. Then I counted "seconds" with the old "one thousand and one, one thousand and two ..." before sticking the case neck in water. Using a variety of counts, I found what number gave me the anneal that I wanted.
Of course, you would not want to do that with hard-to-come-by brass like .45 Colt, .50-110 Winchester, etc., because you ruin quite a few before you get the best count. But, for the cases like .223, .308, etc. that seem to turn-up in droves at ranges, with many appearing unworthy of reloading anyway, that can be a cheap approach.
One thing that I always bothers me about this approach is that I don't seem to keep my count rate consistent over a lot of brass, even though I "calibrate" myself at the beginning of an annealing session. And, looking at a digital timer and then back a the case doesn't help me hold the case exactly where I want it in the flame.
I could make things more complicated by having an actual mechanical fixtrue to hold the drill, but we all know that slippery slope leads to one of those neat machines shown in the posts by jmorris.
I have always wanted to find the old metranome that I KNOW is somewhere in my Mom's attic, so that I could have an easy to use timer with sound "signals" that allowed me to not have to look away from the flame.
Oh well, maybe in some yard sale...