Do not do the exercises for longer than 3 minutes, and at first also not more often than twice a day. The exercise is best done with sunlight and never directly after a meal. We may do this one after the  first breathing exercise, if that has already been practiced for two weeks previously, and we can atb ease make the breath of 7 seconds for three minutes. 

 DESRIPTION OF THE SECOND RHYTHMICAL BREATHING EXERCISE

We are standing upright, with arms hanging down along the body, head erect, chin pulled in just enough to show our independence, the eyes fixed on a point before us, not further away than 2 metres . The body should be fully relaxed, but the spine straight and firm, for the spinal marrow is the seat of the soul. the body's weight should balance on the ball of the feet. To do this gracefully, we let the body gently sway back and forth. Do not rest on the heels. Mouth shut, theb tongue against the lower teeth, like with the first exercise. While breathing, slowly and harmonically for 7 seconds, while we intuitivelyfollow the stream of the breath, we will stand on the toes and place the weight on the point of the feet. Then we bring the body back into the previous position, while steadily breathing, with a graceful movement, that is so easy to do for a controled body. If we are expecting immediate success from this exercise, we will slowly clench the fist while breathing in (N.B.: Omraam Mikhaël Aïvanhov describes this special posture of the hand too, a specific sort of fist) gradually but thoroughly. We clench them more and more firm, but without any effort, without specifically tensioning the muscles or gnashing the teeth. While breathing out we slowly relax the fists, let the body rest again on the balls of the feet, and even if the heels are touching trhe ground, no weight may rest on them. To be able to relax easily, we just have to empty our lungs thoroughly and bend our knees forward some millimeters. Here too: ( after the preparatory Kapalabhati ) breathe inthrough the nose for 7 seconds , hold for 3 seconds, breathe out for seven seconds through the mouth, hold for three seconds, and so on, for three minutes.

Some more explanation with this exercise:

...We may also do this exercise while walking. As soon as we have learned to balance the body to and fro, we will do some steps while breathing in and then try, for some steps, to hold the breath. After several days this exercise will become of uncomparable value, because it evokes the electrical current in the feet, of which our hearing is strongly dependent. Gradually we will develop our hearing and we will, in all that peole are telling us, be able to distinguish between true and untrue. On the other hand we will tell nothing, that cannot stand up to the test of truth. we will also see that our time is much too precious for critisizing others, and with joy we will greet the day on which everyonec will mind his own business - but if we want that, we ourselves must first act, and not wait untill others set the example. We must be an example ourselves, then the othres will then follow...

-third lesson, p.46: ...You should, as we hope, understand very well, that our exercises are a means to an end. When the desired point in the development has been reached, we no longer need to stick to the usual exercises. We expect that this development will bring us to areas that transcend this lower form of existance and teach us how to make use of the knowledge we gathered on our journey, on this terrain of our activity... -p.47: ...Breathing serves to eliminate all shortcomings and to enable us to concentrate. By concentration we do not mean: meditation. We do not attach any value to meditation on a specific subject, that covers but one aspect of our nature. Concentration is something, that considers all that belongs to our immediate happiness. Concentration of our thinking powers is absolutely necessary, but meditation we might, if necessary, be able to do without... We should realize very well, that  none of our exercises should require any effort at all, that we absolutely should not strain ourselves... -p.51: ...If  the people around you get exited, and start loosing their self-control, sit down and breathe. Take a few breaths, concentrate on "Breath is Life" and after a few minutes you will amaze everyone by your calm decidedness and efficient assistance, making everything end well... p.55: ...With insufficient breathing capacity , the lungs may not suffer directly, but other organs will, considering their intelligences, suffer a shortage of supply and this condition is then signalled through to the senses by means of the nervous system that, when forced to exhaust its reserves, will become incertain in its functioning and will keep the senses in a state of uncertainty. this is why often, when we are most in need of our presence of mind, we will not know what to do or how to find a way out of our troubles. Such a condition will come about whenever we are not able to stop the creative working in the nodes of our nervous system by pauses in our breathing. our senses are as much a manifestation of the condition of our body and its activities as of the capacity of breath and brains...

-p.56: ...As long as our attention is mainly on belly-breathing, the intelligences of the lower nature will fully reign the vibrations of the brain, while the spiritual can only surface in times of sickness and then ends in mental depression. Sometimes unconscious too, as if against our will, as proof of the presence of a higher nature, that our consciousness cannot express, because we do not understand our own true being...

...Thus we get near, step by step to the point where it seems as if there is something in this life, that demands our attention and we start breathing with the solar plexus-breath, be it unconscious, when we grow toward it by an urge that is put onto us from outside, in our state of singular being. Then we will go from one extreme to the other, thinking only of the Future at the expense of the Present, just as in our animal state we neglect to seek and dig for the dead bones of Israël. In the material we do injustice to the spiritual and in the spiritual in reverse to the material, by neglecting the needs of thePresent. We shall breathe the breath of life untill we rise above all superstition of this time, towards the areas above - the heaven of the intellectual, that knows peace , love and harmony: a world without end...