From the room with the clock, head out directly into the main hall. There, you will find two guests, who are the people you need to save in this task. You can pass them by and head left on the ground floor. If you wait until they leave the hall, than you might not have enough time to discover the shortcut.
Go through the next few rooms until you find the one with a padlock on a green door. Use Grayson's mask, in order to remove the padlock. Then go through the door.
Go forwards until you reach the room shown in the picture above. Your task is to smash the chandelier . However, in order to achieve that, you must place you hero in the point  indicated in the picture above. Use the door  and head to the upper level.
Follow the only available path, until you reach the chamber shown above. Apart from the door that got you here, you have two possible routes. The first door  leads to the balcony from where you can shatter the chandelier. Do not go in there, and instead, use the second door . In the second chamber behind said door you will find one of the workers, but more importantly, a winding key. You should be able to go in there and take it without any issues around 9 pm.
Then go to the balcony as soon as possible and drop a fragment of the chandelier. Go back down.
First use the lighter, in order to light the candle  that fell from the chandelier. When you do that a ghost will appear next to you . Talk to him, until all of the dialog options have been exhausted, and you will learn that interacting with the bookshelf  reveals the entrance to a secret chamber .
After entering the back room move as fast as you can to the room shown in the picture above. Approach the clock  and fix it. Then synchronise it with the pocket clock. You can also pass through the door marked above , in order to unlock a shortcut, but you can also do that later.