Little late, but just to add to the timeline stuff:
Noriko was already following Sensei around when she was 3:
Wizards are mostly supergeniuses who are seemingly inherently attracted towards Sensei in Kumon-mi, so I wouldn't be
too surprised if Noriko was bothering Niki and Sensei as an infant...
Noriko is confirmed to be 16 at the start:
According to the Care Packages. (Ayane is 15, and Kaori is 22, so it's likely referring to their ages at the start of Chapter 1) Ami should be only around a month younger than Noriko and has a bday early in Chapter 1, meaning she's more or less 16 for most of the game. (The game itself seemingly starting in August. Ami's birth month.)
So, Ami and Noriko were probably born in July and August 2004 since they turn 16 in 2020.
This would mean Sekai and Mama Nakayama were knocked up in 2003, which is when 'Kyoto' should be taking place if Sekai is recently pregnant with Ami.
The Accident happens when Ami is 7 (assuming Sensei isn't rounding):
So it could be as early as 2011, and up to 9 years ago which is probably why Niki compares it to almost a decade:
The last 8 years part probably wasn't counting this year:
Overall: That timeline might be around a year off, but it should be around those time periods when things happened, eitherway.
Except for Kyoto, since it simply doesn't fit if Sekai was just now pregnant with Ami, with Noriko already around, even though she should still be in her mother's womb.
Edit: Unless this 'Kyoto' Happy Event is meant to be some kind of confirmation that Ami is actually around a year younger than everyone, like Rin, and just no one is aware of it. Which could also explain her physical development, if time itself isn't simply deaging Ami to fit Sensei's taboo preference, retroactively, or some crap.