Meditation is nice when it is done intermittently. It makes you feel good and has a calming effect on the body and mind. However, meditation does not show its full potential unless it is done as a prolonged practice. This means regularly, every day or every other day, and for at least a half hour. This is not for beginners, since at the beginning longer sessions of meditation can frustrate people, even cause mental distress. Once you have started to do meditation regularly for a while at a shorter length of time and feel comfortable then you can increase the time and feel out what suits you best.
Meditation retreats, which can range from a day, a weekend, a week, or even a month, include prolonged meditation practice that might involve 8 hours of meditation a day every day of the retreat. This is starting to get into the territory of prolonged practice. This has a dramatic effect on the mind, allows one to truly deepen their practice, and allows the practice to do its more thorough work spiritually. I highly recommend anyone who has been meditating for at least 6 months to try a meditation retreat. It is invaluable to learning about yourself and the nature of your experience.
Seasoned meditators, including spiritual aspirants, might live a life dedicated to this amount of practice. Only this way will they truly transform their minds spiritually to be able to be available to other beings in a most capable and profound way. This may include monks, as well as yogis who live in caves and meditate 24 hours a day.
I am not asking you to live in a cave and become a yogi, unless you are truly called and prepared to. What I am suggesting is that you take your practice to the next level if you can and extend your practice to include longer sessions at more frequent intervals. Instead of only meditating when you feel like it, set a regular schedule, every day if you can. Instead of only practicing for 20 minutes, try extending once in a while to 40 minutes, or an hour, just to see what it feels like to practice for an extended period of time. Try to push yourself to accomplish your best and most thorough practice, while always being completely sensitive to your natural limitations.
Prolonged meditation practice offers the promise of dramatic transformation mentally, emotionally, and spiritually. Taking your practice seriously and pushing your edge a bit allows for a deeper connection and a greater possibility. I encourage you to take your meditation to the next level. May you deepen your meditation through prolonged practice, that you may find a whole new dimension of your practice.