Set the stars, left to right, to 4 2 3.
That is the whole answer. The reason this page exists is the second half: you need this same configuration again after the credits, and by then the attic is many hours behind you.
Where the chest is
Day 1 Night, in the attic, during the Searching the Attic block.
Note it down
The post-credits achievement "You've found him!" walks you back through all three days re-entering specific answers, and the attic stars are step five of eight. Players who did not record the configuration end up hunting for it after they have already finished the game.
The other values that route needs are the clock at 4:05, the Day 2 bathing tiles (Aleksandra, bath, suitcase, severed hand), the Day 3 alchemy sequence, and the cabinet code 6294. All of them are collected on the all codes page, and the full route is on the "You've found him!" page.
Achievements in the attic
Chasing the Crow. Move in and out of the containers in the attic repeatedly until the crow appears at the window, then click it. The clue — "Many things are staring from the window! Click on that bird!" — tells you what to click but not that you have to make it show up first.
Checking for Intruders. Not in the attic itself. Go back to the corridor window where you served the tea earlier in the evening. Clue: "Be Thorough. Are those specters?"
Where this sits
Day 1 Night closes the first day. Continue to Day 2.