I have so far only smoked baby backs which seem to be done in 4-5 hours. Tomorrow I am going to try BRITUing some thicker St. Louis style ribs. I am too lazy to foil, so should I assume a 7 hour cook time at 240?
240? at the lid? Yes, about 7 hours, but it also depends on the size/weight of the rack(s). A smaller rack, trimmed closely, may come in under 7 hours. A bigger and meatier rack may go longer.
I'd start checkin' for finish (tear test) around 6 hours, and go from there, but 6 hours would be the earliest for a small/light rack.