Only time routes matter is at the very end of your third half playthrough. Route A takes you through the whole game, Route B recontexualizes the second half, and then you do that basic thing again and then at the end C and D are both variations that you need to unlock all weapons for I believe. Once you are nearing the end of your C playthrough, you can save before the final part, and do the C ending, and then reload your save for the D ending. Just make sure D is after C. Because uh. Reasons.
