Maybe a month or so, I'd say.
I read the novel for a bit. It was a long time ago, and I could not stomach the EXTREME paranoia, so I stopped. Like seriously, the manga tones down the paranoia a lot compared to the novel. In the novel, he's a complete nutcase, he is even constantly paranoid about the girls.
And I might be wrong, but I'm pretty sure his goal was literally "living with his harem and banging them", and everything related to the labyrinth a tool towards that goal.
So yes, i might have confused the novel and the manga a bit, but I think he really did not care about personal power all that much besides getting enough money to support his harem... Which fair, that's a goal, but I was referring to making getting personal power one of your GOALS.
So either I remember incorrectly (possible) or this part was kinda once again left out of the manga. Me, in his place? I'd be in the labyrinth for power, and even for more power XD