CAT

Undoubtedly, CAT is a tough nut to crack. How much time is required for the preparation to crack CAT depends upon the dedication and smart preparation by the student. CAT has three sections. Quantitative Aptitude, Verbal, Data Interpretation and logical Reasoning. Number of questions in each section:
Quantitative Ability: 34
Verbal Ability & Reading Comprehension: 34
Data Interpretation & Logical Reasoning: 32
Total: 100
Now, actually, most of the syllabus of CAT comprises of what we already studied in class 9th and 10th. And to pass through CAT with flying colors, one requires a good understanding of Syllabus, Time management technique and Smart answering technique. If one prepares for it with dedication then 6-8 months would enough for cracking CAT and getting a call from top most institutes for an average student. I hope that I answered your query well. Good luck.

It totally depends on your choice of institution you want to go in. In some colleges, they take you on the basis of your National Level Examination ( CAT/MAT ) score while on the other hand some institutes conduct their own entrance exam. However, General Eligibility for MBA includes :
1. Minimum aggregate score of 50% (45% in the case of the candidate belonging to reserved categories) in his/her graduation or degree exam from a recognised university.
2. Qualify an Entrance Examination like CAT/MAT/ XAT/CMAT etc. - Some of the universities conducts their own entrance exam too.
3. Qualify Personal Interview as conducted by different institutes. Top Institutes from where you can pursue MBA :
1. IIT Madras, Chennai
2. Lovely Professional University, Punjab
3. Xavier Labour Relations Institute, Jamshedpur
4 Nirma University, Ahmedabad
5. Kristu Jayanti College, Bangalore
6. NMIMS, Mumbai
7. ICFAI Business School, Hyderabad.