Great Worg slain - 27344/38728, 20h6m59s. I would assume this is a night spawn.
I had a (much) higher Paladin friend of mine kill every worg in a 5000 foot radius to try and get him to spawn. It still took us three full game days to get him to spawn. (Thanks, Gwilissa!)
When he did spawn, he was red to me at 14. Took 'em down with my whip.