hi,

see the proficiency gaining depends on your surrounding, your instructors, exercises, timing of classes, your zest for learning a foreign language, how much effort you would given for that particular language etc. generally coaching institute conducts 600 to 650 h classroom program for b2 level, with 3 days a week classes. however to gain the proficiency you would try to read french books   and communicate  in french with fellow students. however based on different opinions of student it would take to 6 month to reach at average level and to master the language may take 1 year.