Thinking about Time-Turners, and for a long time discussing potential implications (for, after all, there's only very basic data in canon), turned out well in the end. My brother's notion that you go back in your own lifetime as well as in time enabled me to give the story structure: the first story I've had an actual outline for in yonks.
It's always seemed to me that Minerva, after the revelations from Voldemort and especially Harry, would be a chastened woman. I imagine she'll spend a lot of time rethinking the last year. She might even be a bit less Gryffindor. And perhaps in 24 years she'll be a glad woman, relieved of burdens at last.
Hermione isn't perfect; I didn't want her to be, but to show her maturing, intellectually and emotionally, learning to be (fairly) calm and open to compromise in her marriage, and to be adult and hands-off with Severus.