Come morning, leave the dining room and head to the western wing of the first floor. Open the door on the northwest of the hall.
Inside the room examine the safe near the window on the left side and enter the password "saeki" to open it and find a key inside.
Now leave the room and head up to the second floor then go to the west wing there and enter the southwestern door.
Examine the large dresser by the window to find another note which is actually a clue for the next key.
Head back down to the first floor and the phone will start ringing. Go to the dining room and pick it up, then exit the dining room and head for the last door on the very right of the hallway to get to the garden.
In the garden head down south and you'll find a patch of flowers that stick out like a sore thumb in the bare garden. Examine it and them out to find a key underneath.
Go back inside the house and climb up to the second floor, then turn left towards the western wing. Use the key on the door at the northwestern wall to enter the storage room.
Examine the right side of the cabinet at the far left corner of the room to find another key.
Leave the storage room and this time head for the easter wing of the second floor, then use the key on the door at the southwestern part of the hall.
Examine everything in the room, I'm not sure if it's required to do so but seems like I wasn't able to trigger the cutscene if I didn't. The computer is the important bit.
Exit the room and head back to the western wing on the second floor. The doorbell will ring as you pass the stairs. Head down and keep going south, interact with the door to answer it.
After Shinji leaves it will be night time and the phone will ring at night. Head down to the first floor and answer the phone in the dining room. Make sure to save your game first before answering it.
When the monster appears, turn left and run into the next room. Then exit through the southern door in that room.
Quickly run up to the second floor and head to the western wing. Enter the door on the southwest, where the dresses are.
Hide inside the cabinet beside the dresser with a large mirror near the window and you'll make it to the next day unharmed.