at least in terms of timeline placement it sure seems to be, with Inko-sensei being a mainstay serialized author now who even got an assistant. I could see it being maybe a couple years after high school, with Tadokoro as an exchange uni student somewhere abroad. Sounds plausible.
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.
"Sakurako looks pretty ghostly when Inko-sensei mentions her. She's still in love, years after the beautiful, heartbreaking, romantic death of the only one she'll ever love, despite what society says. Yes, she'll try to heal her sorrows with her assistant, but that just means one or both of them will die, too! It'll be so beautiful, romantic and doomed! Girls love is too pure for this cruel world!"