I am an avid BBQ roaster and have been for about 8 years now.
Roasting times can vary according to bean type, but I find the biggest thing that changes times is volume of beans roasted.
I currently use a 2kg drum over a 4 burner BBQ. I only use 3 of the burners at the start and reduce this to 2 once up to temp.
Looking at the thermometer in the hood, I usually aim for 260+ up to first crack. Once I get to rolling first, I reduce the heat down to low on the 2 burners. This will usually (unless it is a very cold day) take me to second crack if I want to get there.
Now... the big thing - times.
I roast either 1875g or 1250g batches.
1875g - ballpark timings
1st crack - 15 mins
Rolling 1st - about 15-30 seconds after first
1st crack completes - 17-18 mins
2nd crack - 20-21 mins
1st crack - 12 mins
Rolling 1st - about 10-20 seconds after first
1st crack completes - 14-15 mins
2nd crack - 17-18 mins
Ambient temperature and wind make a difference to me as I roast outdoors. Even though the BBQ has a hood, wind can still penetrate.
Warmer weather, faster roasts.
The rpm of my motor is around 40 these days. It was 55 when it started its' life, but considering the work it has done, I think it is allowed to be a little slower.
I personally think you need to tighten up your times, not lengthen them. If you are roasting less than 2kg of beans, 30 minutes seems too long in my opinion.
If you are roasting less than 1kg, then it is certainly too long.
Feel free to ask more questions. I'm obsessed!