Instance will vary -- see Cel's comment to find out if a specific one has been chosen yet.
Sign up as a member, THEN comment with your class & role. Preference will go to first sign-ups that can fill an empty role. There will be a 5-minute grace period for lateness before replacing a sign-up character with an alternate.
Saturday evening Bitz and Cel will look at the sign-ups and try to arrange the best group they can. See RKC section of website for more details.