(This review contains plot information regarding Harry Potter and the Cursed Child but only very mild spoilers.)
In 2013, J.K. Rowling wrote a short post (since deleted) on Pottermore, the official Harry Potter website, detailing her thoughts about using time travel as a device in literature. In the third book in the Harry Potter series, The Prisoner of Azkaban, Harry’s friend Hermione Granger uses a device called a Time-Turner to attend multiple classes in a single school hour, and the Time-Turner later factors into the plot when Harry and his friends use it to battle Dementors and help Sirius Black escape execution. “I went far too light-heartedly into the subject of time travel in Harry Potter and the Prisoner of Azkaban,” Rowling wrote. “While I do not regret it … it opened up a vast number of problems for me, because, after all, if wizards could go back and undo problems, where were my future plots?”
After Azkaban, Time-Turners were eradicated from Rowling’s magical universe. Hermione returned hers to Professor McGonagall, and all remaining instruments were apparently destroyed in a climactic battle in the Department of Mysteries in the fifth book, Harry Potter and the Order of the Phoenix, ruling out any more time travel. Rowling concluded the Harry Potter series with a natural leap forward, showing Harry and his wife, Ginny, saying goodbye to their second child, Albus Severus, on the platform at King’s Cross as they sent him off to his first term at Hogwarts. It seemed as definitive an ending as any, but it’s at that exact moment that the newest installment of Harry’s story picks up.