Kisukesama is incorrect on the Arch Corse part. He pops in a place where no Arch Corse spawns what-so-ever. If you see an Arch Corse, you need to go further North. His pop area is the area with 2 of the purple/red flowers and 2 scorpions that patrol around them. He can spawn after the 20:00 time, but only if his ToD and night time (20-4)occur after the 20:00 point on the first night. If he despawns, he will ALWAYS pop at the 20:00 mark on the next day.
Drops from Xolotl in Attohwa Chasm.
21-24 Hour repop, around E-7
Will either pop at 20:00, or an Arch Corse will pop instead.
Followed and assisted by Xolotl's Hound Warrior, and Xolotl's Sacrifice.
Much praise to the kote, AWESOME DD piece, especially for monk.
@Ashky: Regardless of if an Arch Corse pops or not, this info still holds true. ;p