How many hours we need to study to clear KAS ??

Get the copy of the syllabus. Through Internet you can get the important study materials required to crack the exam. Buy it. Read through it. Revise, revise and revise and you are good to crack the exam.
If you are OK with attending classes, join a weekend batch in some coaching institute.
From what I have observed these days, a lot of aspirants start preparing right from their graduation days which I think is a good thing as we don't study the graduation subjects everyday.