Ask around how long to sit each day, and you are likely to get many different answers. Some believe, the longer the better. Others like Mingyur Rinpoche, advocate 'short times, many times'. At Zen Hospice, short 5 to 10 minutes mindful checkins before each shift appear to have a significant impact on the well-being of the volunteers and their ability to provide mindful, compassionate care. It certainly did for me. Yet others advocate a middle road. The standard length at IMC is 45 minutes, same as in Mindfulness-Based Stress Reduction training. Ayya Khema recommends a minimum of 30 minutes every day. Intuitively, and also from personal experience, it seems that the mind needs a minimum amount of time in order to settle, and also that the longer, the more settling is to be expected, as in the case during retreats for instance. I make it a point to sit at least 30 minutes every morning. I also do shorter sittings throughout the day, and once in a while, I will do 45 minutes sittings, mostly when I sit with the IMC sangha.
Turning to neuroscience research, there does not seem to be any conclusive answers, or at least not yet.
An important question that deserves more investigation, it seems . . .