Hi.

For an OBC Candidate of outside Delhi region you need a rank lower than 9789 (2020 Round 5 closing rank) for that you would need approximately 150-160 marks.

Now as for the studying part, honestly there is no exact answer. Everyone has their own pace of studying, strong subjects and weak subjects. Although if you wish to achieve such a good rank it is strongly recommended you do not leave any topic since there is no exact weightage of topic from which the questions are built. Conic section, complex numbers are one of the important topics, which if you try can manage in this time. D and F block are scoring topics as well but this is my perspective. Try your best and remember that self-study is an essential element.

If you have a further specific query please feel free to comment.

Best of Luck.