When the new day begins head directly to the room with the elevator and use the door next to it, in order to enter the corridor where you found the winding key.
Once in the corridor, enter the room through the indicated door.
In the room you will find another doorway. At this stage of the game you must peak through the keyhole.
If you came here just after the start of the day, than you will see, that a casino employee is detaching an arm from one of the statues.
When you see this, you must stop peaking. Get out of the room and into the corridor and then go through the next door.
After entering the room ignore all the other objects and approach the curtain. Interact with it in the indicated location. This way you will raise the curtain, and you will be able to peak on the casino employee from the room on the other side of the wall.
Return to the room where you were peaking on the employee through a keyhole. You will have to pass him by on the way there. If you do that in the doorway, than the screen will be dimmed for the shortest time. In the room, use the peep-hole shown in the picture above.
The employee will try to hide the detached statue arm. Watch him all the time, in order to learn the exact location. This knowledge will also be available on the next day, so you do not have to repeat this activity.
Use the time you have left until the end of the day to reach the casino hall shown in the picture above. You will begin the next operations from this point, so synchronize the clock with the pocket clock. Reset the day by using the F1 key.