The general recommendation for practicing meditation is 20 minutes twice a day. As described earlier in meditation on the breath and on the mantra, the procedure is this: 20 minutes of meditation followed by 5-10 minutes of rest. The reasoning behind this is explained by Yogani in the lessons on AYP deep meditation:
When we do practices, we coax our nervous system into a different style of functioning — sustaining deep silence. And in later stages, ecstatic bliss. To stabilize all this we go out and are active in the world every day. There is fading of the higher functioning during activity as we work it into daily living. The fading happens over 5-10 hours. Then we can do practices again and re-establish the higher style of functioning again, to be faded in activity again. This cycle can be done twice a day by doing practices morning and early evening. It provides for the most purification and growth possible during waking hours for people with active lives.
Doing practices once a day is much slower – it is only one daily cycle of cultivating and fading, instead of two. And it is too much fading before reinforcement of the higher style of functioning happens again the next day. Twice daily practice is a matter of effectiveness and efficiency. With twice daily practice over time, the fading of ecstatic bliss in activity becomes less and less, and the higher style of functioning of the nervous system becomes steady and unshakable 24 hours a day.
This is the fruit of the process. It is the ongoing cycle of practices and activity that produces this result.
During retreats, where responsibilities are suspended, more than two routines of practices per day can be undertaken, alternating with meals, light activity, and satsangs (spiritual gatherings). Three or four cycles of practice can be done in this kind of environment. Maybe more for diehard yogis and yoginis. It is a matter of self-pacing for comfort and effectiveness. Then one can go very deep over a period of days, weeks, or months in retreat. This introduces another cycle between retreats that lasts a much longer period of time (weeks or months), superimposed over the twice daily cycle of practices we continue with in our regular life when we are back in the world. Retreats accelerate progress in this way. But retreats are not a substitute for long term twice daily practices at home. What we do every day over the long term is what will make the most difference in the end.
All of this is designed for maximum progress, making the best use of our nervous system’s natural abilities and the time we have available to do the job.