We just gonna ignore that Valkyrie is still going on after all these years? Shit must be at like Bleach levels of content by now
Far from it. From what we know so far, this takes place after she has already graduated (seeing how Hinata states that Inko-sensei-sensei drew Valkyrie "back in high school" and the manga has been serialized "for a few years now"), but it doesn't really seem it's been that many years. According to MAL, Bleach ran for 15 years (and has a few sequels, side stories, etc.); even assuming Valkyrie is a weekly series as well, I'd put it at a third of that at most, but probably less, especially how Inko-sensei-sensei is still picturing Sakurako in her school uniform. We'll see once we actually learn how long it's been - probably when Sakurako returns.