standard answer...it depends: experience is based on challenges and problems you learn to overcome, right? it depends ont he work environment.

if you write reports, you could expect your knowledge of the database and TSQL skills to improve, but not administrative skills like clustering, administration etc.

on the opposite end, if all you do is run backups and make sure they ran, how much do your development and tsql skills improve? you can look back and say "for me, it took x months or whatever, and it might be too long or too short for me, based on my subjective experience in my own environment.