And right now that we only know that Harry’s attempts to travel back in time doesn’t appear to stop Hermione’s death. That could be because for some reason Harry is unable to convince or blackmail Dumbledore and unable to defeat a simple casing despite knowing partial transfiguration, it could be because of an as-yet unstated limitation on the use of time-turners (which would be the bad storytelling trope known as “ass-pull”), or it could be because the same enemy which buffed the troll also takes precautions against counter-turning (for example, by taking meaningless information from 1800, encoding it into the junk DNA of some yeast, and putting the yeast into dinner; I would expect a smart dark wizard to consider something very analogous to this, and it takes a master of stable time loops to go back in time BEFORE eating the food, thwart the troll and save Hermione, then set up a fake troll and fake Hermione so that you can convince the enemy that their plan failed so that they later spend their re-do on attempting to stop yours)
… That was lack of sleep talking.
And right now that we only know that Harry’s attempts to travel back in time doesn’t appear to stop Hermione’s death. That could be because for some reason Harry is unable to convince or blackmail Dumbledore and unable to defeat a simple casing despite knowing partial transfiguration, it could be because of an as-yet unstated limitation on the use of time-turners (which would be the bad storytelling trope known as “ass-pull”), or it could be because the same enemy which buffed the troll also takes precautions against counter-turning (for example, by taking meaningless information from 1800, encoding it into the junk DNA of some yeast, and putting the yeast into dinner; I would expect a smart dark wizard to consider something very analogous to this, and it takes a master of stable time loops to go back in time BEFORE eating the food, thwart the troll and save Hermione, then set up a fake troll and fake Hermione so that you can convince the enemy that their plan failed so that they later spend their re-do on attempting to stop yours)