Excerpt from their book:

“The data suggests that meditating for one session daily is very different from a multiday or longer retreat. Take a finding that emerged unexpectedly in the study of seasoned meditators (9,000 hours average) and their reactivity to stress. The stronger the connectivity between the meditators’ prefrontal area and amygdala (parts of brain), the less reactive they were. The surprise: the greatest increase in prefrontal-amygdala connection correlated with the number of hours a meditator had spent in retreat but not with home hours.

Along these lines another surprising finding was from the study of breath rate. A meditator’s hours of retreat practice most strongly correlated with slower breathing, much more than daily practice. One important difference about meditation on retreat is that there are teachers available who can provide guidance—like a coach. And then there is the sheer intensity of the retreat practice, where meditators typically spend up to eight hours (and sometimes much more) a day in formal practice, often for many days in a row. And many or most retreats are at least partially in silence, which may well contribute to building intensity. All of that adds up to a unique opportunity to amp up the learning curve.

Another difference between amateurs and experts has to do with how they practice. Amateurs learn the basic moves of the skill—whether golf, chess, or, presumably, mindfulness and the like—and very often level off after about fifty hours of improving through practice. For the rest of the time their skill level stays about the same—further practice does not lead to great improvements.

Experts, on the other hand, practice differently. They do intensive sessions under the watchful eye of a coach, who suggests to them what to work on next to get even better. This leads to a continuous learning curve with steady improvements. These findings point to the need for a teacher, someone more advanced than you are, who can give you coaching on how to improve. “