I started with a normal roast profile that started at 375 and increased in temperature as the roast progressed. It took a while to reach first crack and the first crack was weak.
To determine if I needed to increase the temperature, I roasted a batch at 400 to see how long it took to reach first crack. This experiment taught me something interesting: my roaster will not produce first or second crack with temperatures less than 425. This was confirmed in later roasting.
Next I tried roasting at 450. It produced a hard first crack at 4:30, which is too early.