FWIW, I never depend on the roaster. I use a temp probe in the bean mass, and just keep an eye on things. I watch the time, the temp, and listen for FC. I then time from the start of FC and stop the roast when I reach the desired time.
So, I have total roast time, time from start of FC to end of FC (sometimes that's really difficult to measure) and start of FC to end of roast.
I have mine set at #6, and have never had it go to the end. My roasts usually run around 9:30 - 10:00 minutes. Even with the same bean I sometimes get significant differences in roast timings. Ambient temps, humidity, etc. As Jim says, trial and error. And a watchful eye.
I really want to upgrade to the ADR so I have more control. I sometimes think the gas cycles at the most inopportune times.
Jimbo