Here is a great observation by Thomas Keating, founder of Contemplative Outreach. It shifts the focus away from the experience of one meditation session to the “long-term fruits” of silence. How long is ‘long-term’?
In my experience, and listening to others, a week or two of short daily practice is likely to be enough to give you a personal data trend you can start to notice. But that is just the begining…
“Don’t judge centering prayer on the basis of how many thoughts come or how much peace you enjoy. The only way to judge this prayer is by its long-range fruits: whether in daily life you enjoy greater peace, humility and charity. Having come to deep interior silence, you begin to relate to others beyond the superficial aspects of social status, race, nationality, religion, and personal characteristics. (OM, 114)”
― Thomas Keating, The Daily Reader for Contemplative Living