I’m rereading the series, alright. It’s on my mind, let me have this.

Alright rather than handwave it away like people often do, let’s let the canon guide us on how time travel still works in both the original HP series and Cursed Child! (I’m on my lunch break lol)

Firstly we know that the time turner Hermione uses (and the rest of that same stock) are limited to 5 hours because going further than that can harm the user or time. (Source: Pottermore, though admittedly the source was published less than a year before CC’s release so it’s possibly still a retcon rather than pure canon, but let’s allow it for the sake of argument)

We also know that even with the duration limit, it’s still quite possible to break the stable timeline (incidentally the stable “it happened now because you will do it later” effect is known as the Novikov self-consistency principle outside of the HP universe for any sci-fi authors out there, as I discovered while writing this post):

“Harry, what do you think you’d do if you saw yourself bursting into Hagrid’s house?” said Hermione.

“I’d – I’d think I’d gone mad,” said Harry, “or I’d think there was some Dark Magic going on –”

“Exactly! You wouldn’t understand, you might even attack yourself! Don’t you see? Professor McGonagall told me what awful things have happened when wizards have meddled with time…. Loads of them ended up killing their past or future selves by mistake!”

Of course this might only necessarily be an issue the first time you go back in time - i.e. you travel to a time before you know time travel is possible. In any case it is evident that it is possible to change the timeline even within the 5 hour limit.

This means you can have stable time travel if you’re very careful but also means if you are not - such as busting in on your previous self before you knew time travel was possible, appearing in the same place multiple times and confusing the bejesus out of anyone else that doesn’t know time travel exists, or (when we allow CC canon) going back further than time’s mostly stable 5 hours - you can absolutely cause paradoxes and new timelines. The reason it didn’t happen in the books is because they were being super careful barring Harry’s patronus spell - Harry was seconds away from creating a new timeline through his hesitation.

If from there someone were to make a time turner that allows time travel further back in time without harming the user in the process then it still works in canon and still abides by the time travel laws of the HP universe. And indeed that’s what they did:

By August 2020, Theodore Nott, while working for Lucius Malfoy, created a prototype of a time-turner, presumably in the hope of saving Voldemort from his fate. The prototype only let the time-traveller stay in the past for five minutes, although they could travel as far back as they wanted.

Nott eventually created a better and improved model, which let the time-traveller stay in the past for as long as they wanted. They could also use the device to return to the future when needed.

From https://harrypotter.fandom.com/wiki/Time-Turner

Of course these devices were rightly considered extremely dangerous artefacts and heavily controlled, but the canon seems to allow it to work.

Having said that! The thing these new time turner v2.0s didn’t solve for is that unrestricted time travel is a very boring story mechanic if the rest of the story is anything less than epic, and this is why Cursed Child remains the Cursed Sequel.

Thank you for coming to my Teddy L talk.