Can someone explain me the exact meaning of にわたって when used in describing time/ duration? I understand its use for range when we describe space. And I know it can mean something like "over a period of", but I saw it also means prolongation of time. Also, isn't 間 alone for duration? Why do we need にわたって?
So, what is the difference here:
私は ３時間 勉強しました。
私は ３時間にわたって 勉強しました。
Hope you'll understand what I want to say. I'm confused because for one moment I understand it and poof it's gone.