Another great health commandment given to us by the Lord is found in Doctrine And Covenants section 88 verse 124.
124 Cease to be aidle; cease to be bunclean; cease to cfind fault one with another; cease to dsleep longer than is needful; retire to thy bed early, that ye may not be weary; arise early, that your bodies and your minds may be einvigorated.
So, what does it mean to retire to thy bed early? What does it mean to arise early?
When you study sleep in connection with health you find that the ideal amount of sleep is about 7 hours, or between 6 and 8 hours. Less sleep than this is detrimental to your health. And believe it or not more sleep than 8 hours is also detrimental to the long term health of adults.
Sleep studies show that the hours just before midnight have twice the sleep value of hours after midnight. In other words, once it is dark outside, it is the optimal time for sleeping. If you can get to sleep by 9 or 10 each evening you will rest much better than if you stay up till midnight, even if you sleep 8 hours.
It is also interesting to note that the body naturally goes into it's heal and repair mode about 11pm each night. So, of course, if you are still awake doing other things your body will not be at rest to be free to do the healing and repairing that it needs to do.
Therefore if you get to sleep by 10pm and sleep 7 hours, you will be up at 5am. Most people would indeed call that arising early.
"Retire to they bed early, that ye may not be weary." Because we don't sleep as well after midnight, if you don't get to bed before that you wake up in the morning and are still weary (or will be long before the day is over), even if you got 7 hours of sleep.
"Arise early, that your bodies and your minds may be invigorated." Early morning, if you have rested well, is a time when the body is well rested and ready to do hard things. The mind is especially sharp in the early morning, if it has had good rest also. Many people have learned that early morning is the best time to tackle the toughest challenges. It's the best time to find solutions to problems, to set goals, study scriptures, and plan out the rest of your day.
Trust the Lord, and do the things that he says to do, and you will be blessed greatly for so doing.