You can meditate whenever you want, or feel like it. Finding a time, either in the morning, at night, or both, where you can accommodate a meditative practice can help you integrate it habitually.
I believe that the best answer to this question is your own. Ask yourself, “when can you meditate?” When are you able to find the time and space to engage in the breath? For some, 10 minutes in the morning when the children are still asleep might work. For others, during lunch at work. For another, it may be before bed. Realistically, our schedules dominate our lives, and we have to integrate such practices. You can only meditate when you can. If you can accommodate, you will be rewarded.
Science informs us that the mind is quietest when we first wake up in the morning. There are many that hold such a routine which incorporates a meditative practice. I do too. Meditating in the morning allows me to set a good foundation for my outlook and mood for the whole day. Setting good intentions for the day ahead.
The reason for your meditation might impact when you meditate. What do you want out of your meditation? Perhaps you wish to quieten a stress response, sink into the breath. Maybe you wish to develop yourself spiritually, then develop a habitual practice. A good combination is to engage in a practice early in the morning, and perhaps find a minute or more before sleep (there is research that asserts our mind and brain are very receptive just before sleep).
