ExploderWizard
Hero
Looking at my copy of B2, there are the following "bosses":
Minotaur - AC4, 36 hp
3rd level evil priest - AC: -1, 14 hit points
Gnoll Chief - AC3, 17 hp plus his two sons, AC 4, 10 hp each
Hobgoblin Chief - AC2, 22 hp, plus 4 females AC, 6 hp each
Hobgoblin torturer- 3rd level fighter
Ogre AC 4, 25 hp
Owl Bear (probably best avoided) AC5, hp 30
So I don't think 5 minutes is out of line. This was a beginner module, after all.
Don't forget:
Bugbear chief-he fights as an ogre

Kobold chief- he is so powerful that he fights with a battle axe!!

Goblin leader (HD 3) and three guards
Cave B Orc leader-fights as a 4 HD monster and has 15 hit points.
I love B2
