11 days. You can also keep the same tactics as before, just save on the 7th day and don't clear out the Seraphim and don't rescue the hero from the tavern.
That is:
7th day, stand near the Nightmares next to Utopia,
8th day, clear out the Nightmares, raise Ghosts, clear out Utopia, visit the stables, and rush to the Elven Archers,
on the 9th day, clear out the Elven Archers and get on the boat.
10th day. Land on his island.
11th day. Defeat the opponent.
Walkthrough for 10 days.
Do the same for the first 5 days, on the 6th day, only clear out the Cyclops, on the 7th day, stand near the stables and dogs without killing them. On the 8th day, kill the Dogs, raise Ghosts, visit the stables, and the hero runs, clearing out the Elven Archers and gets on the summoned boat, on the 9th day, he lands.
10th day, attack and defeat.
But there are a couple of problems here; for the hero to reach the boat on the 8th day, you need to develop his Logistics skill, at least to the Basics level, and also Pathfinding.
Walkthrough for 9 days.
I think it's very difficult to do, maybe even impossible, at least for me.
Well, let's assume we do the same as for 10 days, only when landing, the opponent must attack you; this will be a very difficult battle, but still, after the battle, it will be the 10th day, and in the table, it will be 10 days. So, I think 9 days won't work.
But 10-11 days could be done without much effort. The only problem is the time, which I didn't have to play.