(RealSimple.com) -- Use your body's natural rhythms -- and a few tips from the experts -- to find the best time of day to work out, see a doctor, go to the post office, and more.

Best time of day to clean the house -- 4 p.m.

You're more likely to whistle while you window wash (and not kick over the bucket) if you do it in the late afternoon. That's when hand-eye coordination is at its peak and mood levels are high, says Michael Smolensky, a professor of environmental physiology at the University of Texas School of Public Health at Houston and author of "The Body Clock Guide to Better Health."

If anyone in the house has allergies or asthma, avoid insomnia-hour and morning cleaning sprees (nasal-allergy symptoms are most severe between 6 a.m. and noon, asthma attacks more likely between midnight and 6 a.m.), and finish well before that person walks in the door.

"It takes about an hour for allergens and dust to settle after you clean," says Martha White, M.D., director of research at the Institute for Asthma and Allergy, in Wheaton, Maryland.

Best time of day to take a nap -- 1 p.m. to 2:30 p.m.

Doctors used to think afternoon sleepiness was the result of a big lunch. "But we've found that in the early afternoon there's a dip in body temperature, which causes sleepiness," says Smolensky.

Just as a similar decrease encourages you to shut down at bedtime, this midday dip can make you crave a siesta. An ideal nap, he says, should last 15 to 20 minutes. More than 30 and you may end up with sleep inertia -- and feel even more groggy when the nap's over.

Richard Schwab, M.D., codirector of the University of Pennsylvania Penn Sleep Center, in Philadelphia, says that early afternoon is indeed when your circadian rhythms (the pattern of physical and mental changes we each repeat every 24 hours) are "more likely to want your body to sleep." But Schwab insists that if we weren't all so sleep-deprived, we wouldn't need naps in the first place.

Best time of day to go to the doctor -- 8 a.m. to 9 a.m., or 1 p.m. to 2 p.m.

You'll spend less time in the waiting room if you book the first appointment of the morning or the first after lunch, says Patricia Carroll, R.N., author of "What Nurses Know and Doctors Don't Have Time to Tell You." "Doctors start fresh in the morning and catch up when the office is 'closed' for lunch." Many lab tests require fasting, so a morning appointment will help you avoid being hungry half the day.

If you're seeing a doctor who performs surgery (orthopedist, gynecologist), ask that your appointment not follow her operating time -- a recipe for serious delays, says Carroll.

Pediatricians' and family-practice offices can get mobbed when work and school let out (5 p.m. to 7 p.m.). And if you leave with a prescription to be filled, try to visit the pharmacy before 3 p.m. on weekdays, when it's least busy -- "which also reduces the risk of error," says Carroll. E-mail to a friend

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