You and the other person who shares your mind are unaware of each other’s existence. You both switch places randomly, taking turns to be conscious and unconscious. This causes a lot of confusion as you have no memory of what the other person did or why. If you have Noctis, you get to be awake all day and night, doubling your time to yourself.
However, if you suffer from hallucinations, your time to yourself is limited by how severe they are. If you possess Mild Hallucination, you have 2/3rd the time to yourself. If you possess Hallucinations you have half the time to yourself. If you possess Major hallucination you have 1/3rd hours to yourself. Once your time is up, you switch places with the other person in your mind.
(Anathema and Personified Powers are not viable for Day and Night.)