There are specific periods of time required to break old habits (or patterns) and develop new ones. Often a student of Kundalini Yoga chooses a specific kriya/meditation to affect a desired change and then practices those for a specific number of days:
40 Days To change or break a habit.
90 Days To confirm a new habit.
120 Days The new habit is who you are.
1000 Days You have mastered the new habit.