I've camped this guy so often I was able to raise the price of a Fishbone earring well over 7000 recently just by locking it down and buying up the cheap ones in the bazaar.
He spawns 5.5-6 hours after you kill him. I've logged in earlier to confirm. It's never before 5.5 hours. You'll need two people to lock down his cycle completely. A student to catch the midnight and noon pops and a shift worker to catch the 5-7 AM - evening pops.
Here's some kill data accurate to within a minute of spawn timer The number is brackets is me just rounding off to either 5.5 or 6
1:01
7:02 (6)
1:04 (6)
6:54 (6)
12:46(6)
6:24
Other data from another cycle
6:10
11:49 (5.5)
5:41 (6)
server reset
12:45
6:18
12:04
5:50
If you're lucky, you can pop in and out without anyone even knowing you were in the zone. This is an easy spawn timer to tuck in your back pocket :)