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 original clock was destroyed, the Tempus Clock II eventually taking its place.
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.
Tempus Clock II
The replacement clock is similar to the original, maintaining the psychic bonds it created, including allowing Cindy Vu to freeze Maggie Yen at will and vice versa. Both Maggie and Kansas Wilkins also bound to the clock, meaning if it shatters they'll be frozen in time. The psychic bond allows Maggie to summon the clock to her side, even able to freeze time or people without actually touching it so long as it is close to her. The range of the clock's summoning distance is unknown but it can cover at least one hundred meters. The clock's ability to freeze time or people when its button is pressed or its bells are flicked remains. The main difference between the original clock and the II is the new one can't create new psychic bonds, so no one else will end up bound to the clock.