Did an Overnight 12# of butt cook in the kettle. Low was about around 40, not much wind. Minion method. Not even 3/4 of a bag of KFB, Pan in the middle to catch drippings. Top Vents wide open, bottom vents about 1/8th inch open. Got temp up to about 220 - 235 and let it settle in. Never looked at it again. Got up in the morning and it was at 210ish. Pulled off at Internal Temp of 190 and wrapped it and coolered it Was outstanding meat.
Another one for you.
Did a cook one Sat. Wind blowing like hell, temp was 39, wind chill was ??? Got grill up to temp, same configuration as above. temp fluctuated from 215 and 260. Meat was AWESOME.
Point is, get to know your cooker, you'll know where you need to be. Both scenarios I had fuel left over and used on the next cook. Either way, It's not the Cooker temp, its the Internal temp that tells you when its done.