They're supposed to be specific problems that you or someone you know is facing while travelling, and in theory, there's a specific objective answer to the question.
SO when someone says 'how many days?', that's fairly subjective. It's actually not very useful to others to describe it as such, because again, it's subjective. I spent 6 weeks in Argentina and felt it wasn't enough, while others I know had a week and are satisfied, and others were there 6 months and wanted more. Each person' experience and needs are different.
It's far better to ask objective-styled questions. The above one could be - How Long should I allow for this in Tokyo, and list the activities you want to do, places you want to see and what you want to achieve. Then the previous travellers can use this to answer and assist better.
For example: Is two weeks enough time to drive from Tallinn to Stockholm and have enough time to see the cities inbetween? is a better one, as people can look at it logically, tell you you're driving over 200km a day and let you know how long you might have in each major place you specify.
In general, the more specific you can be in asking your question, the more accurate and useful the answers are likely to be.