Just helped a guildmate with this part of the ranger epic recently. While we were gathering, another guild killed Jaeil the Wretched, so we had to wait for him to respawn. Since no one seemed to know his pop rate and it wasn't posted here, we waited and timed it. It took 6 hours for Jaeil the Wretched to respawn so we could trigger Jaeil the Insane. I hope this helps others who may be doing the ranger epic.
Safe Hunting,
Ruding Cove, Champion
Azure Guard, Veeshan