Quick Answer: Your body runs on a roughly 24-hour clock that times temperature, hormones, alertness and sleep. For someone who wakes around 7 AM, cortisol climbs after waking, alertness builds through the morning, a dip arrives in the early afternoon, physical performance tends to peak in the late afternoon, a "second wind" shows up in the evening, and melatonin starts rising a couple of hours before bed. Here's the day, hour by hour.
These times are typical for a 7 AM waker who goes to bed around 11 PM. If you're a night owl, shift everything later; if you're an early riser, shift it earlier. The free chronotype visualizer shows how the curve moves for each chronotype.
5 AM: Your Coldest Point#
Core body temperature reaches its daily low, usually a couple of hours before you'd naturally wake. This is when sleep is hardest to shake off, and it's also the pivot point for light: light before it tends to push your clock later, light after it pulls it earlier. More in the phase response curve.
6 to 7 AM: The Wake-Up Surge#
Melatonin is falling and cortisol is rising. In the first 30 to 45 minutes after waking, cortisol rises sharply; this is the cortisol awakening response, part of what gets you moving. It's normal, not stress.
7 to 9 AM: The Light Window#
Daylight reaching your eyes now is the strongest signal your body clock gets all day. About 20 minutes outside sets the timing for tonight's sleepiness. Never look directly at the sun; just be outside. The morning sunlight calculator shows today's sunrise and when to step out.
9 AM to Noon: Climbing Toward Your Peak#
Body temperature rises and alertness builds. For many people, late morning is the best time for demanding, focused work.
1 to 3 PM: The Afternoon Dip#
Sleep pressure has been building since you woke, and your clock's alerting signal briefly levels off. The result is the familiar slump, whether or not you ate lunch. A short walk or a 20-minute nap helps more than another coffee; see why you crash at 2 PM and the nap calculator.
3 to 6 PM: Strength and Reaction Time#
Body temperature approaches its daily high, and many measures of physical performance, such as strength, flexibility and reaction time, tend to be at their best in the late afternoon and early evening. A good time to train if your schedule allows.
6 to 9 PM: The Second Wind#
Oddly, the hours before bedtime are often among the most alert of the day. Researchers call it the wake maintenance zone: your clock pushes hardest against sleep just before it lets go. It's why you can feel wide awake at 9 PM after being exhausted at 3; the second wind explains more.
9 PM: Melatonin Starts to Rise#
In dim light, melatonin begins rising roughly two hours before you'd naturally fall asleep (this is your DLMO). Bright screens and ceiling lights hold it back, so this is the time to dim things down.
11 PM to 3 AM: Deep Sleep First#
The first half of the night is richest in deep, slow-wave sleep, when growth hormone release peaks and the body does much of its physical repair.
3 to 7 AM: More REM#
The second half of the night has more REM sleep, the stage most linked to dreaming and emotional processing. Cutting a night short at the end costs you mostly REM.
These are averages. Your own timings depend on your chronotype, your light exposure and how much sleep you owe. A consistent wake time keeps the whole schedule stable.
Where ARC Fits#
ARC plans your day along this curve, shifted for your chronotype: a 20-minute light timer from your real sunrise, a last safe coffee from your own bedtime, and a wind-down reminder before bed. After about ten days of one-tap check-ins, it measures when your afternoon dip really lands instead of assuming 2 PM.