Decent story until you introduced Oren and the random Slytherins. They make no sense, aren't driving the narrative, and are genuinely uninteresting people. Please leave them out of the rest of this story if possible because they're detracting from what was a perfectly enjoyable time travel story. Also, Oren is a completely abhorrent human being who is somewhere between sociopath and political activist. He decides unilaterally to save the life of one of the most incredibly dangerous people on the planet because his life happens to be tied to something with historical value. It's like going back in time to save Hitler's life so you can preserve him in a museum.
Author's response
WARNING: SPOILERS, sort of
I had originally expected more readers to react this way to Oren, but that didn't happen. You have correctly grasped his values, or at least part of them. He's not supposed to be, strictly speaking, a "good guy", and I had intended readers to be wondering what the hell the snitch-spell was thinking.
The trouble is that I wanted him to be complicated enough to be sympathetic to some people, so that where his values diverge from the reader's, it should be troubling. (He absolutely _thinks_ he's a good guy, of course, and _I_ find him sympathetic, but I'm his creator.) He has turned out to be a more sympathetic character than I expected, though.
This is my working theory: Fan fiction readers tend to be very forgiving of certain personality traits and values, even where they don't share them, and that's exploitable. I have exploited it many times over in this story. For example, if I had made Oren plan to burn the books in the Room of Requirement instead of saving them, he would be instantly disliked by nearly all readers. Book _burning_ is a known and extremely effective trick for reducing sympathy for doggedly sympathetic characters. I would not stoop to using it directly, but I did manage to (unwittingly, at the time) use its reverse. If you save books, you can eat babies (try it in your next story!). The same goes for a lot of other things Oren does if you keep reading.
I will definitely not be insulted if the story isn't to your tastes! I do, however, really appreciate that you reviewed anyway, since now I know at least somebody took issue with Oren's plans. :P
EDIT: Why use an original character?
Because I wanted a Slytherin, I needed them to be at Hogwarts in 1990 but still overlap with Harry as much as possible, I needed them to be plausibly sympathetic, and I needed them to not be an idiot. That eliminated all canon characters; if I had waited a year, I would still be stuck with characters who have too much baggage and who readers have preconceptions about. So Tracy Davis and Daphne Greengrass were out, and anyway I want to use them for other things. With an OC who was a pureblood and Slytherin, I could start from scratch and use them as an excuse for a lot of exposition about the wizarding world in general and Slytherin in particular.
There are so many other Slytherins because the only canon characters around in 1990-1991 are quidditch players who the books portray as one-dimensional morons. There would be no one for Oren to interact with if I were stuck with Miles Bletchly and whoever.