Hello dear student, it's never about the hours it's never about the hardwork but it's about the smart work that you do to crack NEET.  But if you study effectively everyday for 5-6 hours you can easily crack NEET . Try to cover the whole syllabus and the most important topics that comes every year . For biology just read ncert as much as you can. As for the biology section questions directly come from ncert . I hope this was helpful for any  further questions and concern . Best wishes