Poison master doesn't have an ICD.
It uses your condition duration and condition damage despite your pet applying the condition when not merged. Because the poison counts as the ranger applying it, it also procs predator's cunning. Of note, your pet proccing refined toxins does not proc predator's cunning. It also uses pet condi duration and dmg. I'm not sure if this is a bug or intentional that these two traits function differently.
So 8 seconds base duration. If the ranger has 100% poison duration, your pet (or SB F3) applies 16 seconds of poison with poison master. Eagle and Hawk have that 6 (4.75) second CD on F2.
That's a lot of poison but you have to give up wilderness survival. I'm going to mess with it in PvP. I'm not sure if this makes condi ranger/unmerged SB more viable in PvE.