You can meditate when you want to, or when you decide you should, or whenever you can sneak it in. It is up to you. The basic principle is to meditate before periods of activity, so that your ability to work and play and socialize can be enhanced by the relaxed alertness in which you are learning to function. The standard approach is to meditate soon after arising in the morning and then again before the evening meal. This works well for a lot of people, and it creates a beautiful feeling of rhythm to a day.
Other options are to meditate once a day in the afternoon or to have several mini-meditations throughout the day. If you meditate before sleep, keep it short and select meditations that are soothing.
Excerpt from Meditation Made Easy book by Dr. Lorin Roche.
