Tried looking at older posts but didnt find it, so forgive if this issue has been resolved
But what was the deal with the girl changing the clock when she first arrived back at the house, and why were there so many of the same two outfits???
Only two parts that leave me scratching my head.
When Sumi first returns home from the hospital and she enters her room, she notices that the clock has been stopped at the time of su-yeon's death (subconsciously 'cause she is still in denial), hence she is being startled. Then, she continues acting as if nothing happened (she chooses to forget) and she sets the clock to the correct time and initiates its function again.
The film shows us the time of se-yeon's death two or three times.
1) When they all hear the sound of the closet falling and the camera focuses on Sumi sitting at her desk reading. On the wall we can see a clock with the exact time.
2) When she has a nightmare about Suyeon's death and the closet falling, we see the time again. She then wakes up, goes downstairs and sees the big sack that she believes it contains Suyeon's body.
3) I am almost certain that we see the time of Suyeon's death one more time in the film, but I can't remember when exactly. But then again, maybe I'm wrong.
About the outfits:
Sumi, while in the stepmother mode, had already put the dresses inside her closet, as well as the diary in her desk, before going to the room for the first time as herself, Sumi. Due to her schizophrenic disorder, she couldn't remember any of that and she thought that the stepmother (who didn't exist in the house at that point) did it. In the same pattern, while in the Sumi mode, she put her father's clean underwear on the bed and when she went again to take them while in the stepmother mode, she thought Sumi did it (herself).