I think it depends on the school.. The school I'm looking at has two full semesters, then a couple of summer classes, one lasting longer than the other, but none lasting the entire summer (2 months tops).. So two semester plus change.
Some school's probably have 2 semeters total, and I've seen a BRN program that last three years.
You see, anyone in a BRN already has their RN licence, so probably 98% of them are practicing RNs... So some schools drag it out as to make it easier on working nurses. I'd rather just get it over with as fast as possible.
In a nutshell, it depends on the school..