Spider has like, what, 8 legs at their best day? So that means 7 vagonois at least, which if mathed correctly, it would be 7x9 = 63 months, which means 5-ish earth years for human.
Maybe the bosses felt sorry because they had believed that harlot's lies and made things difficult for Haru. Not saying he wouldn't have deserved to get promoted, but if the execs had a few good candidates to choose from, and Haru was one of them, they might have thought he's the one most deserving because of that incident.