If you want a single example of the relation of in-game time and real time, I've spent nearly 28 hours in a game year. According to the in-game clock, I've spent 37:33 through Year 2 Summer 11th, which works out to 151 in-game days, or 18.3 minutes per in-game day.
I don't recall leaving the game running alone for any considerable amount of time. I like to plan what to do on the next day, focusing on doing specific things. I have slept many days before 2 a.m. and many other nearly at 2 a.m.
On this Steam Discussion, some players say 25, 30 or even 40 hours spent per in game year. This may not be highly accurate data, being from few players in a game with innumerable gameplay styles and many things to focus and spend time on.
So, if you want more accurate and statistical data, I would recommend you creating a poll of in game time vs playtime on some game discussion forums, asking for personal experiences (I couldn't find much on this online).