Dear candidate, preparation time varies from person to person. However, regular study of 6-8 hours is mandatory and solving questions from previous year papers leads to smart study. It is considered that a period of 2 years, that is, after class 10th boards is the best time to prepare for JEE. In short, five months are not at all enough for good preparation of JEE Mains exam. For more information, you can check:

https://engineering.careers360.com/articles/jee-main-preparation-tips

Hope, it helps!