Earliest possible encounter? (Possible racing spoilers.)

[Sexbad]

Since some of the game is nonlinear, there are places you can go in any order that have illusions. Daniel does

Spoiler below!

The Archives contain an imaginary monster. I believe that after the cave-in you can re-enter a room with a doorway that is blocked off by rubble and a monster will appear behind you. You can also go to the Wine Cellar and pick up a specific bottle of Laudanum and a monster will appear at the end of the hallway. I'm not sure if the latter is imaginary, though.

and then she gives him a restraining order.