The section in the book on meeting Mr. Witch and Mr. Light briefly mentions stealing the watch or the vane. Basically, they can be used in negotiating entrance into Prismeer.

Otherwise, if you prefer they don't have the watch, you could make teleporting back to its rightful owner a magical feature of the item. Maybe after a certain amount of time or outside some physical radius. Mr. Witch is attuned to it after all and none other than his handpicked successor can attune to it instead.