Aslam,
There really isn't an "average" that is correct. Everyone is different. Some people study for 4 weeks and pass the exam, while others study for 4 months and still fail.
As a general rule: Study 5 days a week - 1 hour every day - for about 12 weeks.
I wrote a series of 8 articles describing the complete journey. Please read them to understand the complete process. The first one is here:
www.cio.com/article/626983/How_to_Prepar...ess_Your_Eligibility