From my experience, I have seen people writing exam with just 3 days of crash course and scoring 8 band,
and people taking 2-3 months time for studies and not scoring even 6.5-7 band.
So, I feel, its all depending on,
1.how many hours u spend on studying,practicising?
2. how dedicated you r?
3. how far your grasping power developed??
4.how much time you allow yur mind to be in English pool in a day, sort of watching english movie, or newspaper , magazine,etc??
So, It is not important how many months u need to study??
how well u prepare on each day, how confident and positive u r counts so much than other criteria.
So go confidently, you will do excellently....wishing u all the best.