The Time-Turner

• Type: Magical Device, Time Transportation
• Owners: Ministry of Magic, Hermione Granger (on loan)
• Maker: Unknown, but their creation and distribution are strictly controlled by the Ministry of Magic.

A Time-Turner is a magical device used for time travel. The one used by Hermione Granger is described as a tiny, sparkling hourglass set in a pendant on a long, fine gold chain. It is small enough to be worn as a necklace and concealed beneath one's robes. The hourglass itself contains glittering, sand-like particles.

The primary function of a Time-Turner is to allow its user to travel back in time. The mechanism is straightforward: one turn of the hourglass corresponds to one hour of travel into the past. To operate it, the user places the chain around their neck and the necks of anyone travelling with them and then turns the hourglass the required number of times. The use of Time-Turners is governed by strict magical laws and carries immense danger. Professor McGonagall warns Hermione Granger of the grave consequences of meddling with time, recounting tales of wizards who accidentally killed their past or future selves, driving them mad. The most critical rule is that a time traveller must not be seen by their past self, as this can cause profound confusion and damage to the timeline. The model of time travel presented in the novels is a closed-loop causality model, meaning that the past cannot be truly altered. Any actions a time traveller takes in the past were, in fact, always part of history. This is demonstrated when Harry Potter and Hermione Granger travel back in time; their “interventions”—such as Hermione throwing a rock through Hagrid's window or Harry casting the Patronus Charm to save Sirius Black—were events that their past selves had already experienced without understanding their origin.

Time-Turners are extremely powerful and dangerous objects, and their use is restricted by the Ministry of Magic. To be granted permission to use one, as Hermione Granger was, an individual must have an impeccable record and a very specific, Ministry-approved reason. In Harry Potter and the Prisoner of Azkaban, Hermione is granted a Time-Turner by Professor McGonagall to allow her to attend multiple classes scheduled at the same time. She uses it discreetly throughout the school year. In Harry Potter and the Order of the Phoenix, the entire stock of Time-Turners held by the Ministry of Magic is destroyed during the Battle of the Department of Mysteries. During the fight in the Time Room, a shelf containing the Ministry's supply is hit by a spell, causing the glass cabinet to shatter. The Time-Turners fall and smash, only to magically restore themselves and begin falling again, getting trapped in an endless time loop. An Unspeakable later confirms to Cornelius Fudge that the entire stock was destroyed, effectively removing this powerful magical tool from the world.

The Time-Turner plays its most significant role in the climax of Harry Potter and the Prisoner of Azkaban. Following instructions from Albus Dumbledore, Hermione Granger uses her Time-Turner to take herself and Harry Potter back three hours into the past. Their mission is to save two innocent lives: Buckbeak the Hippogriff, who is scheduled for execution, and Sirius Black, who is about to receive the Dementor's Kiss. They successfully untie Buckbeak and lead him away moments before the executioner arrives. Later, they witness the Dementor attack on their past selves and Sirius Black by the lake. Harry, realizing it was he himself and not his father who cast the powerful Patronus he saw earlier, successfully repels the hundreds of Dementors. Finally, they ride Buckbeak to the tower of Flitwick's office and rescue Sirius, allowing him to escape from Hogwarts. The destruction of the Time-Turners in the fifth book is also a crucial plot point, as it prevents an easy solution to later tragedies, such as the death of Sirius Black, and forces the characters to face their problems without the ability to reverse time.

• On the Pottermore website, J.K. Rowling explained that she deliberately destroyed the Ministry's stock of Time-Turners in Order of the Phoenix to close a significant plot hole. She acknowledged that if they continued to exist, readers would wonder why Harry didn't use one to prevent events like Voldemort's return or his parents' deaths. (Pottermore)
• Rowling also established further rules for time travel, stating that the longest a person can safely travel back is about five hours, and any longer risks serious harm to the traveller and time itself. She wrote a cautionary tale about a witch named Eloise Mintumble who was trapped in the 15th century for five days, which caused irreparable damage to the timeline and resulted in twenty-five of her descendants “un-birthing” from existence. (Pottermore)
• The play Harry Potter and the Cursed Child introduces a different, more powerful type of Time-Turner that is a prototype capable of travelling back years and creating alternate timelines, a direct contradiction to the closed-loop system of the original novels. (Harry Potter and the Cursed Child)