So!
I've just finished the game in 7 days, though I'd found out about it due to a YouTube playthrough in the first place, so the completition time doesn't really matter.
But, to revive this forum a bit, I've decided to give you more info about the game itself, a bit of a Q&A for the curious pals out there! Of course: there will be major spoilers. If you want to play the game at its fullest, don't read this post yet.

Minimum amount of days to complete the game: 7. During your first staying, you can't get your hands on a knife until the end. You can hide it in the umbrella stand, but you won't be able to proceed. The butler won't give you another, and the owl will refuse to talk to you. The only way to continue is to kill the owl. Second cycle, you can get the second knife. Hide one, use the other, and you will reach your third playthrough with a knife at the beginning of the seventh day. The fail point is when you first talk to the owl: do it, and it's game over. For now.

Types of food the butler can cook: haggis, mashed neeps, porridge, lamb and kidney pie, scotch broth.

Names of the protagonist/owl: Riley, Dawson, Fowler (owl?), Chambers, Webb, Brown (only the owl, beginning of the game).

There are several different voicelines when you begin a game after x cycles:
2 cycles: "This place looks strangely familiar."
3 cycles: "There goes another one."
4 cycles: "This place looks strangely familiar. Like I remember it from a weird, long forgotten past..."

There appear to be only two items: the contracts, and the knife. You can have two knives, but only after the first playthrough. You can't hide the documents or a second knife inside the umbrella stand.

The telescope does nothing, apart from a short text cutscene.

There's no limit to the days that can pass.

That's it!