concentration

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Yes it does matter, you will feel more rested if you go to sleep and, wake at as close as possible to the same times each day. That's because of our Circadian Rhythm, a sort of internal clock that controls all sorts of things like hormone release, body temperature, when you feel alert or groggy and more.

Here is an brief overview, explaining the basics.
http://www.nigms.nih.gov/Education/Facts...hythms.htm