Coffee roasters should be concerned about when and at what temperature they turn off their coffee roasters.
It’s good to understand why we should wait?
And then we can understand when to turn off our coffee roaster?
WHY? When a coffee roaster is roasting coffee the heat applied raises the beans to 200°-210°-220°-230°C. That’s 400°-420°-440°-460°F! That’s really hot. If you immediately turn off a coffee roaster when the drum is SO HOT the force of gravity alone will pull the round drum to slowly become oblong. And we all know that an oblong (non-circle) does not roll very easily or evenly.
The metal drum inside your roaster is round - it should be nearly perfectly round. Let’s not discuss the possibility of a perfectly round circle, which many dispute can ever exist.
For a circle to be perfect, we would need to measure an infinite number of points around the circle's circumference to know for sure. (link Carnegie Mellon University & College of Science)