Larry, what I generally do with the Hottop fan is to bring it on 50% power for about 30 seconds between 3-4 minutes into the roast (suck out the moisture). I then leave it off until about 6-8 minutes in, when I set to 25%. About 10-12 minutes in (right before first crack), I push the fan to 50%. It generally stays there, unless I need to quickly slow things down--that is, the temp ramp gets too steep after first.
I don't do that much, and I don't do that during 1st crack, as you can easily stall things out as the beans through the end of 1st crack.
I've got some graphical software coming that I'm going to use to build some HMIs--one of the displays I REALLY want with the hottop is bean mass temperature rate of change. That's the main thing I am calculating in my head as the roast progresses.