Sri Chinmoy: The best time for meditation is early in the morning. When you get up, that is the best time. If you get up at 5:30, that is the best time. If you get up at 6:00, that is the best time. If you get up at 9:00, that too will be the best time, but you have to know that at that hour you will be swimming against the current. By that time the world has become full of noise and activities; everything is hustle and bustle. But if you get up at 5:00 or 6:00 or 7:00, you will still feel poise and peace in the atmosphere. So the earlier you can get up, the better.
Now, the length of time depends on your capacity. If you can meditate well for fifteen minutes, then do so. But if you just sit at your shrine for two hours, although your mind begins roaming after ten minutes, that is of no use. As long as you can meditate soulfully, you should meditate. But if you are just dragging it out and watching the clock to see how many hours you have meditated, that is of no use. If you can meditate well for fifteen minutes in the morning, that is more than enough.