Let's face it: Some days at work it seems all you do is watch the clock. From the tick at 9:00 to the tock at 5:00, it's just a coast-to-coast flatland of interchangeable hours, spiked dead center by the glorious 60 minutes that is lunch.

But before you go scheduling a month's vacation or unearthing those old motivational tapes, take a deep breath and think for a minute or two about how to make every hour count. By timing your daily tasks to match your physical and mental energy levels, you can give yourself more energy, less stress, and a better sense of accomplishment when it comes time to knock off.

YOUR BODY CLOCK

Start by remembering that when you watch the clock, the clock is also watching you-the circadian clock, that is. Your body is actually influenced by 24-hour programming created in the part of the brain called the suprachiasmatic nucleus, or SCN. This is where the gears, dials, and springs of your circadian clock are wound by evolution to turn and click in response to light and dark.

In addition to timing your sleep-wake cycle, your circadian clock also regulates the cycles of body functions, such as hormone secretion, body temperature, blood pressure, and kidney activity. And while it means you'll usually feel most sleepy between 2:00 and 4:00 am, the clock's 24-hour cycle also makes you feel naturally sluggish between 1:00 and 3:00 pm-the middle of our modern workday.

To make your circadian clock work for you instead of against you-and to take advantage of other biological fluctuations going on inside you-take a look at this list of "power hours" that can help make your day more productive:

Best time to do the hardest thing you'll do all day: early morning. Several hours before you wake up, the stress hormone cortisol rises, which increases your blood sugar level and gives you the energy and momentum to manage difficult situations effectively. Though too much cortisol can make you feel overwhelmed, it also contributes to that "fight-or-flight" ability to finish pressing projects-or to ask the boss for a raise.

Best time to make a presentation: 10 am. Your voice is most rested, naturally, in the morning when you wake up. And by 9:00 or 10:00, you've had a chance to drink some water and give your voice box the hydration that helps eliminate early-morning raspiness. Before speaking to that assembled group, get the vocal chords vibrating by speaking aloud-or even singing a quick tune, even if it means hiding for 5 minutes in the bathroom.

Best times to stretch: 10:30 am, 2:30 pm, 4:30 pm. Stretch every few hours to avoid the back and shoulder tightness that comes from hunching over your keyboard. Clasp your hands behind your back, lift them straight up, and hold for 10 seconds. This opens your chest and relaxes your shoulders and back. To stretch your chair-bound glutes, cross your left leg over your right, resting your left ankle on your right knee. Bend forward at the waist, and hold the stretch for 10 seconds. Then switch legs and repeat.

Best time to make major strategic decisions: late morning. Your body temperature is rising, your alertness is up, and your brain's ability to process information is at its peak. Experts think that the body's rise in temperature may keep your mind more aroused, so it's also a good time for solving problems.

Best time to read dense reports with lots of facts and figures: early afternoon. It's hard enough just after you wake up in the morning to see out of half-lidded eyes. But your vision actually remains blurry in the morning and takes several hours to sharpen up. By afternoon, your eye muscles are more flexible, and you're seeing much more clearly.

Best time to snack: 2 pm. Give that circadian clock a couple of raps by beating your midafternoon slump to the punch. A snack well after lunch, but just before your clock revs you down, will help you ride out the slump and keep you focused. Try eating a handful of nuts; the protein will increase your energy, and the fat will keep you full until dinner.

Best time to drink coffee or take a walk: 3 pm. Remember that caffeine can screw up your sleep by interfering with hydration levels, stomach acid production, and kidney function. But if you're hooked on java, allow yourself a quick jolt of 8 ounces or so about 30 minutes before a midafternoon meeting to help keep you awake. If you've sworn off coffee or soda, take a brisk 15-minute walk around the office halls. You'll help restimulate the hormones associated with alertness.

Best time to make or return phone calls: 3:30 pm. Simple tasks can help you stay focused and productive until the bell rings at the end of the day. Getting some person-to-person stimulation by telephone or even by answering some e-mails will help you finish the afternoon strong but still help you dissipate stress that has accumulated during the course of the workday.

Best time to tee off with clients: 4:50 pm. Typically, hand-eye coordination reaches optimal levels in the late afternoon, so put it to good use by squeezing in nine holes or a few sets of tennis before the sun sets.