Knitted should blanket needle size/length

Hello,
This pattern calls for a size 17 circular needle, but I was wondering how many inches should the cord be? Any suggestions? Thanks! Jaye

http://www.joann.com/content/projects/static/spring06/knitted_shoulder_blanket.pdf

for casting on 36 stitches just about anything that is comfortable will work. i like 24 inch personally.