When do I have to apply for an internship?


Hi everyone,
I would like to know when is the right time to apply for an internship in one of the Big four for the summer or for Fall Semester.
I live in the USA but I think it might be the same process as GB.

Also, I was wondering approximately how long was the process from the application online to the potential position offer?

I visited the websites of the 4 and they’re always talking about leadership and being a leader and that freaks me out a bit as I have never been a leader -neither follower. I guess I’m right between the two but is it really important to show them your leadership skills or is it more like a preferable asset for them?

Thank you!