So that's why that path of boards is available down there! I've used it, but never even thought about what it would be like in an aurora. I've only been down in the power station from the main entrance, while an aurora was happening - and, of course, there is a hallway with pipes that is impossible to get past while an aurora is going.
RE: time period - I think I read in one of the Mailbag posts that the decline of the island started before the Collapse, so there's not a clear time period for where we are, playing the game, based on artifacts found. The tombstones, though, do at least put an upper limit on things.
My personal head canon remains that The Long Dark in Survival Mode is what happens to Commander Shepard after the end of the Mass Effect trilogy (if you choose Reaper destruction, and then imagine Shepard recovering, only to go down in a plane over Great Bear Island). 😉