anything is possible, maybe 3-4 hours a day depending on how much time you have, use your study periods, it will be essential.
make sure you have one day where you don't do anything at all, take breaks, hydrate, exercise, go for walks, GET EIGHT HOURS OF SLEEP, eat three meals a day to keep your mental health up if you are going to go all out. It's okay if you don't achieve it, the only person you have to prove yourself to is you if that makes sense, but if you really want to get those grades make sure you are doing it for yourself, at the end of the day it's only a letter so please don't work yourself up over it, work hard and do your best is all I can say.