There are two ways to interpret this question. One, as a broader question about what stage of your life you should begin a meditation practice. The other, as a specific time of day to begin meditation. I’ll try to answer both.
Broadly speaking, the answer is right now. As in, start meditating today. There are so many reasons your mind will find to avoid meditation: you’re too busy, you’re not ready yet, you’re not calm enough, you don’t know how to do it right, and on and on. But as Patanjali’s Yoga Sutras teach us, “Yoga is now.” In other words, there is no need to wait for permission or the right stage in your spiritual development to start meditating. Meditation, like yoga, will meet you wherever you are – that’s one of the best things about it. So, let go of the excuses and just start today. (Learn how in Meditation 101.)
As for the second question of timing, the answer is based on your personal preference. Many people, myself included, value meditation first thing in the morning. I like to get up, have a cup of tea and do some gentle yoga stretches to make sure I’m fully awake. When my body feels relaxed and open enough to sit in a meditation posture, I start. This works for me because I feel like it's a great way to start my day with a complete reset. I have the opportunity to check in with myself, and it helps me to cultivate the centered presence that I hope to sustain throughout my day. (Read more in Morning Rituals for Yogis.)
For other people, meditating first thing in the morning might not be feasible. So, make it work for you – there is honestly no wrong way to do it. An alternative time might be as soon as you get home from work. This can help you to mark a boundary between your “work time” and “personal time” and help you to reconnect with yourself after a busy day. As long as you’re meditating, you’ll be getting the benefits. (Learn more about Trusting the Practice of Meditation.)
Late evening meditation can also be very special. It’s an opportunity to pause before going to sleep and allow yourself time to just be. Meditation can help calm and soothe your mind, so it's ideal if you’re suffering from insomnia as it gives you a chance to wind down and relax. You might want to begin in a seated meditation, then lie down for the last few minutes and meditate in savasana.
Be open to the fact that different things work for different people. Experiment a little to find what works for you. Just remember that the most important thing is that you do it. The time to begin your meditation practice is [some time] today.