Around 6 months to prepare spending 4 to 5 hours in a day. Apart from k & B, I reffered khalid mughal for study material. For mock exams, I used Whizlabs full version and enthuware beta edition. Both of the mock exams simulator are rocking. And two mock exams that were provided with K& B book.
One advice : Try to attempt as many mock exam as you can.