SCORPIUS
Professor Croaker’s law – the furthest someone can go back in time without the possibility of serious harm to the traveller or time itself is five hours. And we went back years. The smallest moment, the smallest change, it creates ripples. And we – we’ve created really bad ripples. Rose was never born because of what we did. Rose.

Harry Potter and the Cursed Child - Chapter 2 :
See this quote in the Pensive -