I am convinced that the window of time which produces fully developed coffee while not sending too much out the smoke stack is narrow. I'm not convinced that it is contingent upon the final temp of the coffee, though it could be. It seems to me that you can roast a batch to a temperature that you are typically uncomfortable with - whether low or high - as long as you are in this narrow window, and produce incredible coffee.
I say this in context of my other posts - that there is a proportionality or balance to the entirety of a roast. You can't roast recklessly and drop the batch in the narrow window and expect a good coffee. There's nothing magical about the window of time; just because something comes out of the roasting door in that time frame doesn't make it something it's not.
On our roaster, I'm finding that any coffees over 14:00min begin to lose body and unique character; it flattens out, takes on generic flavors, and even the light coffees have a roast note. Conversely, roasting coffees under 12:30min seem to lack depth and taste as if they were roasted too aggressively. That leaves you with a 1:30min window.
A time frame for roasting coffee is not an innovation. Coffee roasters have known for a long time that a roast which is too long or too short adversely effects the cup. What is new to me is that the window could be so narrow. I have followed profiles that have been as long as 16:00min, and others that have been as short as 8:00min (ignoring home roasting in a popcorn-popper altogether). But as I have roasted and cupped batch after batch on our UG-22, I can say that there are some clear boundaries for finish time: 12:30-14:00min. I doubt that these are the same exact parameters for every machine, but I do believe that each machine does have a narrow window.
I'm happy with where this leaves me. I want to find boundaries to narrow down the possibilities - whether that's time or temp retrains for the entire roast or just one phase. Systematically learning the roaster and how to use it makes me able to control the roast for the purpose of the cup. I want to be able to know general rules for our machine in order to manipulate the flavor of coffees.
My end goal is to know things like: what does a 3min vs a 4min Browning Phase do? That question becomes much more difficult to answer if the possible finish time spans 8 minutes. It feels impossible to answer. But if I know that I prefer the flavors that come from a profile that is balanced and proportionate, and I know that I will drop coffees between 12:30min-14:00min, then the question regarding a minute difference during the Browning Phase becomes much more attainable.