In HPMOR, time travel obeys the Novikov self-consistency principle (with the exception of liberal use of deus ex machina to keep it from being over-powered). If it were possible for Harry to use a time-turner to save Hermione, she wouldn’t have died in the first place.
In HPMOR, time travel obeys the Novikov self-consistency principle (with the exception of liberal use of deus ex machina to keep it from being over-powered). If it were possible for Harry to use a time-turner to save Hermione, she wouldn’t have died in the first place.