Next to impossible to evaluate, it depends on way too many things and most of those are about yourself.

For an experienced, but relaxed replay I would set aside something between three and six. One can probably speed-play in under an hour, haven't tried, but would believe. One can take many more, it not too unusual to spend up to an hour for a single game year sometimes, or fast clicking trough a decade in less than half that. And, no, it won't necessarily average out.

Most importantly, for your first play you will spend a lot of time reading, learning and probably restarting, the game may appear very hard at first, it takes time before you form the right mindset to accept and enjoy it.

It isn't a game you play through once, it's meant to be replayed many times, enjoying the experience not pursuing a goal.

As a full newbie, for me it was 12 hours

I'd say 10 to 20 hours - but it's really hard to tell, really depends on what's happening in the game.