it’s mentioned in the chapter I think that it’s a year and a half between the 228 and 229

The end of 228 just says “several years later”. Besides, a year and a half feels a little short considering by then their old teacher has two children, the older of which looks to be about 2 or 3 at least. I was thinking it was closer to maybe 3 or years. By then Shuu and Ruri are a teacher and a translator, which I think requires some time spent at university.