I know that Bloodtalon is not on a timer, because about 30 minutes after my group killed him on Friday night, he spawned again.
Some people say that you have to kill the Centaur Captain if he is up, or else he will prevent Bloodtalon from spawning. This is not true, because the Centaur Captain was up both times when Bloodtalon spawned.
Mighty Griffon is supposed to be the placeholder for Bloodtalon, but we killed all the Griffons anyways. It took us about 1 hour to get him to spawn the first time.