You can practice meditation at any time of day or night; but try to establish consistency. Meditation benefits you most from being performed every day at the same time and, if possible, in the same place. Traditionally, the morning is considered the optimal time because you are less likely to be distracted by the demands of your day. When you wake in the morning or before going to bed at night are times that lend themselves well to a period of stillness and reflection. However, afternoon or early evening is also fine. Wait at least a half an hour after eating - up to three hours after a heavy meal - so there will not be competition for energy between digestion and meditation.
The best way to start a meditation practice is to sit daily for five to ten minutes. After the habit has been established, gradually lengthen the amount of time in five-minute increments. Short, regular sessions are fine, and better than infrequent long sessions. After some time, you will probably sit for longer periods and discover the pattern that suits you best. You may add 5 to 10 minutes of meditation at the end of your yoga practice, or do 15 to 20 minutes or longer independent of your yoga practice.
When not to Meditate:
Don't attempt to meditate at a time of day that is always busy, or if you are over-stimulated by caffeine or alcohol, because you may well be distracted. You may fall asleep if you are tired, or after a big meal. If you're feeling depressed or even just a little blue, it is not a good time to meditate. If you are filled with negative feelings, meditation could actually concentrate them and make you feel worse. The physical action of doing some yoga postures will move impurities and negativity out of the body. Meditation is best practiced in a positive frame of mind.
It is helpful to create a special place to meditate; to create a certain simplicity around you that reminds you of the importance of giving care to your inner being. If possible, find a place that is somewhat secluded from excess noise and disturbance, one that is pleasant and warm. It may be simply a corner of your bedroom that becomes a dedicated space. A friend of mine, that has several children, practices meditation in her closet with the door closed! Turn off the telephone and television and as much as possible create an external space of silence and calmness. But, try not to worry too much about any external noise. There will always be some noise beyond your control. Use earplugs if external noise is disrupting your concentration. If meditating outside, choose a place where you feel safe and relaxed, and there is little extraneous activity to disturb you. Practicing outside in a place of natural beauty makes it easier to relax and prepare the body for the peaceful side of meditation.