1. Studying for an exam – 8 AM or 10 PM
Students stay late up at night not just to cram for an exam, actually without even knowing it, they take advantage of the body’s circadian rhythm. Professor Michael Smolensky of University of Texas School of Public Health says memory depends on nucleic acids and these peak and valley at certain times within 24 hours, so the best time to read and retain would be eight in the morning or 10 in the evening.

2. Cardio Workouts – 5 PM to 6 PM
Accoring to Matthew Edlund M.D. early evenings are great for cardio workouts since this is the time of the day when your lungs use oxygen more efficiently and your body is more coordinated. Your muscles are also pretty much warmed-up so there is a less chance of muscle injury.

3. Taking A Nap – 1PM to 230 PM
We all feel drowsy after lunch, this is because of our body rhythm that repeats within a period of 24 hours. The dip in body temperature every noontime would be ideal for a 15-20 minute nap, according to Richard Schwab, M.D. from the University of Pennsylvania. However, a nap greater than 30 minutes would make you groggy instead of feeling refreshed, so turn on that alarm.

4. Cleaning the House – 4 PM
Hand and eye coordination is highest during late afternoons, according to professor Michael Smolensky of the University of Texas School of Public Health. During this period you can take advantage of your high mood level to do chores such as cleaning the house, doing the laundry, etc.

5. Taking Vitamins – Breakfast time
Vitamins are found in food, so even if it is water or oil-based, it is best taken with meals. Specific vitamins keep you awake so it is much advisable to take your daily supplements during breakfast.

[source http://www.realsimple.com/realsimple/gallery/0,21863,1053802-1,00.html]