I'm a bit unclear about the timeline. Is this the summer vacation time directly following season 2 - which, if I remember correctly, ended with some school's out celebration - or has more time passed since then? Depending on that, how does the first russian scene relate to past seasons? Is this something that happened after the events we saw, or concurrently or even leading up to them?
I did some reading to understand the timeline better myself. From what I understand, season one happened in 1983, ending around Christmas time. Season two happened the following year (1984), occurring around Halloween. Season three starts in June 1985, where we see the Russians trying to reopen the portal that Eleven closed. And we jump forward a year later (1986) where we catch up with the entire cast.