"You arrived there just in time."
Translation:Tu y es arrivé juste à temps.
Y means "there", but it's used more like the-place-we-have-been-talking-about.
For example: Est-ce que tu es allé à Prague? (Did you go to Prague) Oui, j'y suis allé. (Yes, I went to that place we have been talking about just now, which is Prague)
"There" here implies someone knows where there is, someone mentioned it before. This is why the answer has "y"