That's fine JBord but you still make an assumption when you say, "people who have similar interests'. You might for example say you like hiking and want to do some in the Davos-Klosters area of Switzerland. As someone familiar with that area, I could give you suggestions as to where to find information on hiking in the area (although you could just as easily find that yourself with Google) but I could not and would not attempt to tell you how many days to spend in the area. An interest in hiking simply isn't enough for me to know how interested you are. I could spend 2 weeks there every year for decades and not be bored or feel I have 'done' it all to my satisfaction. Someone else might consider having done 3 one hour hikes in the area enough for them to then want to move on to somewhere else. That's why I say you go, you stay till you are ready to leave and then you move on. I don't try to guess or assume how long it will take you to reach that point.

I do not look at other people's opinions as to how long to spend in a place, ever. It tells me nothing about how long a place will hold my interest. A travel forum is great to get answer to objective questions for which you have not been able to find the answer through your own research. i.e. 'Does the Davos train station have a left luggage facility?' But as soon as you enter the realm of subjective answers (opinions), you are asking for a crystal ball answer and I don't know anyone who owns a working one.

The OP has asked a seemingly 'simple' question. I have X time, want to visit 4 places, how long should I spend in each? But it is a question for which there is no simple answer and no way of anyone being able to give an answer that is relevant to the OP personally.