Details From Harry Potter and the Cursed Child That Make No Sense
It Changes How Time Turners Work
In Harry Potter and the Prisoner of Azkaban, we learn exactly how time turners work from one Hermione Granger. Namely, we learn that their capabilities are quite limited, and can only be used to go back five hours without causing irrevocable damage. What’s more, there’s no mechanism for traveling back to the present. Instead, you just have to wait for time to reach the present again.
In Cursed Child, though, both of those rules are changed. Now, time turners allow you to change the past and then return to the present, which is not at all how they work in the books.