Yogic science says that there are specific lengths of time needed for certain desired effects during meditation. Most meditations are done for 11 or 31 minutes, but there are many variations on time.
3 minutes of meditation affects the electromagnetic field, the circulation, and stability of the blood chemistry.
11 minutes of meditation begins to change the nerves and the glandular system.
22 minutes of meditation balances the three minds (negative, positive, and neutral) and they start to work together so your mental integration changes.
31 minutes of meditation allows the glands, breath, and concentration to affect all the cells and rhythms of the body. It balances the 3 gunas, 31 tattvas, and all layers of the mind's projections.
62 minutes of meditation changes the gray matter in the brain. The subconscious "shadow mind" and your positive projection are integrated.
2 ½ hours of meditation changes the psyche in relation to the surrounding magnetic field so that the subconscious mind is held firmly in the new pattern by the surrounding universal mind.
© The Teachings of Yogi Bhajan, Aquarian Teacher KTI International Kundalini Yoga Teacher Training Level One Textbook
 Tattwas: qualities associated with earth, water, fire, air, and ether