It isn't an official stat, just been monitoring it with /who [targetname] or /who game the past few months to see how many players are online. Also using:
http://laanx.fragnetics.com/index.php?page=char_statsto check to see who is online and how many are playing. Offtime is more like weekdays-afterwork/night playing, not really when most everyone is asleep or at work. And I'm not positive on the EU Offtime stat, since I only play around that time when I take a day off of work. Does seem they have a bit bigger audience during their evening than US, may be way off on that. I have definitely seen a pickup as the confidence and stability in the server has been pretty good since the last big crash. Course we'll see if that theory is accurate as fragnetics has been out of commission for almost 24 hours now. We'll see what kind of population we get when it comes back online. Ah, fun stuff.