Consider medicalised meditation as a treatment and follow the instructions given by your health care practitioners. Spiritual meditation practice offers much more freedom but it has a spiritual rather than a wellbeing goal.
There is no simple answer to the question. Most medicalised meditation forms have been studied over relatively short periods, eight or ten weeks, for example. And three or four sessions a week is a fairly typical level of practice. Few scientific studies reliably explain the cognitive mechanisms underpinning meditation’s benefits, and we have even less data regarding the optimal frequency and duration of meditation in clinical contexts. From the scientific history of meditation and mindfulness, it appears that experiments used eight to tend week cycles of treatments on an arbitrary basis, and that has just been repeated ever since. As a starting point, you should ask your meditation teacher or Doctor to explain if more meditation is likely to be helpful in your particular case.
Although the use of meditation in a medical context assumes that most people meditate in a similar fashion and receive the same benefits, this is far from true. Individual differences are amplified during mind-training. While one person may experience little benefit, someone sitting right beside them can be transformed by the practice. Typically, in scientific studies, we average the effects of meditation across a group; this makes it hard to predict the benefits of medicalised methods in individual cases. In thinking about the frequency of meditation practise, we need to consider; the current state of your health, the particular technique you use and your overall capacity as a meditator.
Things are different when we think about spiritual-based meditation. It’s not unusual for experienced Buddhists to meditate more than once a day or for several hours at a stretch when on a retreat. But in many cases, experienced practitioners have developed their ability to meditate over many years. Secondly, they are likely to be meditating for spiritual rather than wellbeing goals. Buddhists access methods that are supported by hundreds of years of anecdotal and observational experience. A traditional meditation master may have taught tens of thousands of students. In contrast, some new forms of meditation and mindfulness have only been around for a short time, and the data supporting their clinical use may be based on studies of just a few dozen people. However, even in spiritual practice, there are occasions when too much meditation can be counterproductive.
An important distinction to make here is that traditional meditation is often regarded as a practice, which means it is not the goal. Instead, the meditation method is likely to lead to new ways of thinking more generally. Medicalised forms of meditation and mindfulness rely on the method itself as the treatment without the support of more broad-based changes to the patient’s world view.