Hey guys, been reading the forum posts with interest and thought I better get my act together and finally contribute!
I installed the plus upgrade panel about 3 weeks ago and have been enjoying the manual control, it sure does add some extra excitement to it all. I'm not hugely experienced in the roasting department, however I got the impression the idea was to back off the power at or just after the first snaps of first crack. With the 1600, I hadn't been too adventurous and had stuck with using 300 g on the 1 lb-P2-B profile. Sometimes I would get first crack near the drop in power that Rider referred to. Other times it would be much later, and on cold days I was getting close to running out of roast time before onset of second crack.
Since running the plus panel, my approach has been to roast 300 g using the 1 lb-P1 (100% power) profile, which initially gives you 18 minutes roast time. At the 1st snaps of first crack (or shortly after), I drop the power to 75% (P4 button) and then hit the C button (Rosetta Stone feature). This resets the clock to 3:10, and as lukemc indicated, if you need further roast time, you just press the C button again to give you an additional 3:10 minutes roasting time. That is some peace of mind when you are roasting and shivering out on the verandah in the cold!
Anyways, with my 300 g batches I haven't had to stretch things much beyond an 18 minute roast time to get to second crack. The recent batches I've done of a KJM-style blend have been around 15 minutes to first crack, and a further 3:20 to start of second crack. I've done a couple of batches of Zambia Terranova (I really like this bean), and it got to first crack at 13:30, and a further 4 mins to second crack.