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Will taking a year off/redoing a year from UG hurt my chances for Oxford PG

I am studying Philosophy with Psychology at the moment, meanwhile I am taking as many modules as possible to do with AI, maths, etc (Neuroscience, Neural Computing, Philosophy of Mathematics, Logic metatheory..). In 2nd year at the moment, got a first in 1st year.
I want to get into a top university for postgrad studies for Neuroscience or Computer science (I want to work in the crossection between the two in research). Oxford in particular has a very good Neuroscience masters who has apparently accepted others from my course.
However due to mental health (and some physical health) reasons I missed out a large part of this year leading me to have to defer my exams until Sept. But things didn't get better so I am considering redoing year 2 so that I don't just mess up my exams and therefore ruin my chances of getting a good grade, which I will need especially as I'm competing with Neuroscience, Maths, etc students.

I was wondering if anyone knows if this will affect my chances of getting into those Oxford? It will be really clear, even if I get a first, that a 3 year course took me 4 years. I'm really worried.