TV Shows on Itunes - how soon do new episodes become available?

Is it unusual for a new episode to take a week after it airs to appear on Itunes?

The show in question is a kids' show, Zoey 101. My niece has been waiting for it for a week now and it hasn't shown up. The first three seasons of this show are on Itunes, but the first episode from the new season is not there yet. It has been a week, so does this mean they won't be putting the new episodes on Itunes anymore, or is it simply taking longer than usual?

Thanks for your help.