Alright, thanks for making me feel not-as-bad about my failure. I would rather do the main quests "in order", but if he's harder than the quest 4 and 5 bosses, might as well wait (and I read he doesn't get stronger as time goes by like the others?)
The first power up for enemies happens at day 7, I think you'll be finished with the other main quest by then.
Don't count too much on that shortcut though, I sure as hell didn't find it, had to takle the whole tower again.
That's really the biggest problem of the game: you think 12 days will be short, but in the end, you'll finished most doable (at least somewhat interesting) things by day 7 or 8.
So then it's 4 days wondering what you could be doing...