I was surprised to see anyone asking about respawn time on this guy, since I always found him waiting any time I came by. Except, of course, when I showed up with a bunch of friends to finish my 2.0. Bah! So I camped an alt there to watch for him.
The very next time I looked, some nights later, I found him up. I rounded up the usual suspects and we hit him with two full groups which was way overkill, though one caster did manage to take aggro long enough to get killed. (The KoS version summons, by the way.)
Anyway, since I had the alt sitting there anyway, I went back and checked occasionally until I found him back. He hadn't repopped after 4.5 hours, but when I checked again at 6.5 hours he was there.