That depends on your department and your field. Even though, on paper, I had a year to pick an advisor, I worked with mine from day 1 (or day -n since he first

That depends on your department and your field. Even though, on paper, I had a year to pick an advisor, I worked with mine from day 1 (or day -n since he first sent me research papers and discussed ways to get started on my project before my first semester even started). My department was fairly small, though, so you getting admitted meant at least professor specifically was interested in you joining. Professors at larger schools will put on their website not to even contact them unless you have been admitted, and their departments are large enough that only a portion of faculty members are involved in admission decisions. In that case, your advisor of choice may not know about you at all before you enroll and thus you need to fight for a spot in their group among your cohort.