Generally speaking, it doesn't matter what your seniority is - the most senior CA and most junior FO can expect similar (awful) schedules. Seniority doesn't mean much around here.

This is the case more so now with the new 'PBS' type scheduling system. After the "computer" generates the schedules, the company goes back in and assigns all the open flying to our schedules (not in order of seniority, either)..