It has to be dark enough to not be able to see yourself within it to turn you. You could also just partially turn and keep your sense of self if your strong willed or it could just kill you if your frail enough. They emerge from the darkness when its night or if its dark enough in the area for them to stay out of direct sunlight.
Viewing post in This is interesting! Would like to run it.
I announced the game in the Eternal TTRPG Jam server today! It'll be run between the 14th and 20th. If you're in the server, let me know your username so I can ping you in the thread! In addition, you're welcome to sit in on the session; either way, I will be recording it for you and the designer of our setting/dungeon.