The sentence "Time..." is in response to a question from Hermione about how H&C knows Harry will turn dark and destroy her, not in regards to anything having to do with the conversation itself.

Also if you reread the passage in question, you'll see several hints that indicate a long time passed for Hermione also, even though she didn't remember it, e.g. *"Her hand was almost slipping on her wand, there was a sense of fatigue in her fingers like she'd been holding the wand for hours instead of minutes", and ofcourse the fact that the rush of adrenaline at the beginning of the conversations corresponds to the rush of fear at H&C decloaking at the end.