On this page of the guide, you will find out where to find a pocket watch in Twelve Minutes. It is the main element of the story.
The pocket watch is the item that the "policeman" comes for to you. Giving him this valuable relic is not enough to get a good ending. However, finding the watch allows you to do many things and adds dialogues. So it's best to have it from the early stages of the game.
To find the watch, go to the bathroom. Check the cabinet next to the door and examine it, then look at the bottom of the screen. A ventilation grille is there.
Use the house key from your inventory to unscrew the bolts in the grille. After opening it, you can pick up the watch - first signed as "object". It is slightly to the right of the center of the screen - because of poor visibility, you have to aim blindly or use a candle from the kitchen table and put it in the ventilation grille. Note - you have to open the grille with the door to the bathroom closed - otherwise, the wife, seeing you tampering there, will leave the apartment offended.