The game takes place over the course of a few weeks or perhaps a couple of months; the passage of time in seasonal terms doesn’t play a big role in the story (though the epilogues of some of the endings involve graduation, presumably in the spring).
I don’t want to spoil the exact details of the endings in public, so I’m not going to put the info here (even in spoiler text). However I’d be happy to offer that information via PM (as it seems Computermania would be as well).
As le nuage says, none of the “bad ends” are really that bad - nothing that would swing the game into dark territory in a sudden or unexpected way.