If you're here for the safe password, there are 3 hints that point to it in Winter. 

1.  Alle said that her appetite is low in Winter because it's not a good season for her. 
2. There's a snow globe with a Christmas Tree  in it, Rutile mentioned that it looks out of place. 
3.  Her diary implies that her mom died a day after a "Joyous Occasion." 

The code is 2612, a day after Christmas.
My friend mentioned the fact it's in DD/MM and not MM/DD might have thrown people off too...that's my bad. 

- Go to the kitchen, check the cupboard and do the cooking minigame.
- Go to the library and clean the dust in the corner. 
- Go to your bedroom and sleep. 

SUMMER
- Check the cupboard.
- Check the door. 
- Do the cooking minigame. 
- Go back to the kitchen and check the cupboard again to make some lemonade.
- Go to the 2nd floor and give the lemonade to Alle in her studio.

FALL
- Go to Alle's bedroom and Clean two spots.
- Go downstairs and check the door, talk to the milkman.
- Clean the Living room.
- Go to sleep. 

WINTER
- Do the cooking minigame.
- Go upstairs, find Alle in her studio. 
- Go to the library and clean.
- Go to the living room and check the table where you previously cleaned in fall. (The one with the receipt for green paint)
- Go to the library again and check Alle's diary. 
- Go to the Alle's bedroom, check the table and unlock the safe (2612)
- Go to the abandoned bedroom.
For ending 1, keep choosing yes until the end.
For ending 2, stop halfway. 

Hope this is clear enough!