Check March 20th, the bottom text of the calendar, and the symbols on the edge of the calendar's back side.
Summary
Luke and the main character arrive at the escape room, reflecting on their past enjoyment of the hobby and future plans for others before receiving their tickets and instructions for the puzzle. They're to play the role of two detectives in 2046, helping an android named Zero recover its memory.
Through examination of the android's recurring calendar notification and the photos in the room, they determine that Zero first met someone important on March 20, 2033 at the Amusement Park's Surf and Sand ball pit. They're surprised to find the door opens with ease and decide they must be meant to leave the venue to continue solving the room's riddles.