I thought this was me asking, and I asked again after your "gold" ask.
But that doesn't matter.
Thomas carries the key on him Tuesday, Thursday and Sunday's so he can unlock the door straight after work without going upstairs first. The key isn't the hole on those days.
Your file starts at 3:30 pm on Sunday. Skip to 6 pm, then skip to 6pm again. Bringing you to 6pm on a Monday. Go to his room and search the hole.
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It'll be your and I's Secret on what your MC's name is, but I left a letter there so you could see it was your file. I had hoped for a bigger mystery to solve.