I stop it most times when 1st crack is rolling. I let it sit for a minute, then cool. Mind you, I'm trying to find a balance between filter and espresso for my home use.
Not trying to give away too many secrets, but just a tip for those of you out there looking to manage profile or "S" curve roasting.
Many of you have read the theories on endo/exo-thermic transitions of the bean during roasting cycle - so I wont repeat it here.
To manage around these transitions, you need to consider "lag effect".
If you want to move more carefully between the endo/exo stages, you need to play with your heat or airflow in the lead up to the stage, e.g. anticipate when first crack is about to happen and slow the thermal momentum down before reaching it, e.g. not much good doing it once it has started, etc.
Similarly, a common mistake made by some people is they "back off" once FC is underway, only to stall when the FC Exo-thermic stage is over and the beans are once again taking in heat. It's only natural for people to think or act this way - what they see and hear.
In other words, take your actions "before" the stages so that you can move through with control, rather than trying to respond as the thermal lag built-up within the beans are only just starting to "display" mostly once it's too late.
Of course, this all depends upon your roasting equipment and how responsive it can be to your "controls" - try to develop an understanding of the lag affect for your roasting device.