It depends entirely on your previous preparation strategy. Let me tell you frankly you can complete your entire bio,phy,chem within 21 days if you have a fair idea of important topics of each chapter. Revise again and again
Solve numerical problems utmostly. Cover important topics first. Almost syllabus of neet and boards are same. So revise 12 first and try to score maximum in those questions
Reminder. …persistence ,hard work, talent, calmness and destiny complements the function of one another. All the best.