Curious, how hot is your charging temp and how long for your BT to get up to 300F or 149C? My development time is very similar for 230g, but I reach 1st C right around 10 minutes. I do use a variac and have insulated my roaster among other mods. Thanks in advance.
I too have insulated my roaster, and replaced the heating element in September 2015. I use a wide range of charge temps, anywhere from 225F up to 425F. The time to first crack varies widely for different coffees that I roast.
For this particular bean I charged at 275F:
230g load - hit 300 at 6:30, took 11:40 for 1st crack, 14:10 total roast time
200g load - hit 300 at 5:50, took 10:20 for 1st crack, 12:50 total roast time