An ELL post says
The difference here is that there is no inference you expect him to come back more often once the study has completed.
I don't think I understand what the difference is. Maybe it is the difference among 3 original example sentences. Maybe it is the difference between the meaning with "since" and "while".
So, I asked the nice answerer
the difference is between which and what?
I am aware it is not idiomatic at all. Maybe it is not even grammatical. So, how to ask that difference in the idiomatic way?