The Tempus Clock is a magical item created by Maggie Yen using the Book of Tempus. The clock possesses magical powers that allow it to manipulate time and become psychically-linked to its users. The clock is currently destroyed.
Each piece of the clock was enchanted via spells to be sensitive to the very flow of time, thus the manipulation of it allows one to stop time. The clock, according to the book, was supposed to be a sundial with bells attached, but Maggie instead used a basic alarm clock with two bells. The button in the center of the clock stops time when pressed, freezing everyone and everything save whoever is touching the clock. Pressing the button again unfreezes time.
The left bell (left being if facing the clock's front), when flicked, will freeze whom or whatever the person is thinking about. This ability can be tricky to use if the person that flicks it isn't focusing clearly, which can result in multiple targets being frozen at once. The right bell is the counter-bell, unfreezing whatever the user thinks of. The right bell can be used when time is frozen.
It was discovered that the clock is more or less psychic, being linked to the creator and anyone else who used it long enough. This allows the owner to use clock without actually needing to touch it and even summon it a short distance, but if the clock is destroyed those linked to it freeze.