The frequent users of Pixeljoint can go to this page to vote yes/no (or abstain) :
http://www.pixeljoint.com/pixels/icon_queue.asp
Your piece is obviously finished and well done, so most people will not hesitate to vote yes, and thus when a moderator reviews the list (once per day maybe ?), there is a significant number of "yes" and not a single "no", so he accepts it.
Some pieces stay for a long time because they are borderline : people are hesitant to vote yes, but at the same time it's not a case of "definitely not", so they don't vote at all. These pieces stay in the queue for long time, until there are enough votes to help a moderator take a decision.

Mods view/review/add whenever they are online. Your piece is fantastic and would be added even without any member votes because its good work.
Please be patient with us. We are artists too that happen to moderate the gallery.
Should any piece of your in the future happen to be in the queue for days and days and there are no comments in the piece regarding issues of any kind then PM any Mod (about us page) and ask :)