I’ve come to think that the fact that you meditate is more important than when you meditate – the right time of day is whenever you can make it happen. What I have found, though, is that for me, mornings are best, and the earlier the better. It’s partly that it sets the tone for the day, but mainly that it is just much easier for me to finish a sit with less fidgeting before my day has gotten started.
Sometimes, though, in the middle of the day it is helpful to just push the reset button. It may not be as peaceful as first thing in the morning, since I am trying to clear out what has been happening so I can focus on the next part of my day, but if I stick with it, it can do the trick.
A lot of people say the same thing about meditating at the end of the day, to help them sleep better and leave the concerns of the day behind. I can relate, but for that I have a different ritual (a topic for another day).