Answer which doesn’t break established characters: A death eater disguised as Dumbledore lied.
Answer that I can think of that is the least bad: Quiirrelmort steals !Harry’s time-turner and comes back from 6PM to spill the soup and provide an alibi for how he suppressed the wards of Hogwarts (which have been established to detect sudden serious injury of a student- that’s why Malfoy had to die slowly), and used the troll to kill Hermione for the purpose of turning !Harry into the person who has the motivations required to complete the intended narrative.
Easy answer: Dumbledore lied.
Answer which doesn’t break established characters: A death eater disguised as Dumbledore lied.
Answer that I can think of that is the least bad: Quiirrelmort steals !Harry’s time-turner and comes back from 6PM to spill the soup and provide an alibi for how he suppressed the wards of Hogwarts (which have been established to detect sudden serious injury of a student- that’s why Malfoy had to die slowly), and used the troll to kill Hermione for the purpose of turning !Harry into the person who has the motivations required to complete the intended narrative.
Dumbledore teleported by pheonix. I don’t think a disguised death eater could do that.
Yeah, that solution solves the immediate problem by introducing a much larger one.