It is actually stated in the guide.
- "Rumor about the beast" conversation done with Bernard, then with Logan, Rose, Harold, Blake
- "Learn more about werewolves" study back at home (To unlock the event one day must pass after learning recipes)
- 2 Wolf's Bane in inventory
- Happens between 21:00 and 23:59 when entering Bareshade (At least day 30)