Arrange according to physiological rhythm and sleep cycle

In an era where sleep deprivation is almost an honor, finding the best sleeping time may feel like a luxury rather than a necessity. However, science tells us that sleep time is just as important as sleep duration. Aligning our bedtime with our natural circadian rhythm and sleep cycle not only enhances our sense of rest, but also improves our long-term health, mental clarity, and daily performance.

This article will guide you to understand the scientific principles behind the optimal sleep time and help you determine your ideal bedtime.

Understanding the circadian rhythm: the internal clock of the body

Your circadian rhythm is a natural internal process that regulates the sleep wake cycle, repeating approximately every 24 hours. It is controlled by the suprachiasmatic nucleus (SCN) of the brain and is influenced by light to regulate the release of melatonin, temperature fluctuations, and the timing of various physiological processes.

Usually, melatonin begins to rise around 9 pm, reaches its peak at night, and decreases around 7 am, promoting wakefulness. Sleeping during this natural window allows your body to synchronize with the most restorative mode.

Disruption of circadian rhythm - commonly seen in late nights, shift work, or screen exposure at night - can lead to insomnia, fatigue, and long-term health problems such as metabolic disorders and emotional instability.

Sleep cycle: Why 90 minutes are important

Sleep has cycles, each lasting approximately 90 minutes, including:

• Phase 1: Mild Sleep (Transition Period)
• Phase 2: Deep Light Sleep
• Stage 3: Deep (slow wave) sleep
• REM sleep: dreaming and cognitive processes

These cycles are repeated 4-6 times per night. Waking up during the cycle, especially during the deep or rapid eye movement phase, may lead to sleep inertia (dizziness). That's why your sleep duration and time should be planned around these cycles.

Sleeping at multiples of 90 minutes (e.g. 7.5 hours=5 cycles) usually makes waking up more refreshed.

We discussed this point in detail in Why is a 90 minute sleep cycle the most effective.

Ideal bedtime: based on science, not habit

So, when is the best time to sleep? For most adults, a good window is located between 10:00 and 11:00 at night. This time period is consistent with the secretion of melatonin, and one can sleep for 7.5-9 hours before the typical wake-up time (such as 6:30-7:30 in the morning).

For example, if you plan to wake up at 6:30 in the morning:

• Sleep goal: 7.5 hours (5 cycles)
• Ideal bedtime: 11:00 PM

People who sleep earlier, such as the elderly, may benefit from sleep between 9:00 pm and 5:00 am, which is consistent with the age-related changes in circadian rhythm.

Adjust bedtime by age and time type

Different age groups and time types (you naturally tend to be an "early morning lark" or "night owl") can affect the optimal sleep window:

Best Sleep Time Guide for Different Age Groups provided detailed segmentation.

Night owls may require structured schedules, phototherapy, and behavioral adjustments to adapt to typical social times, especially at school or work.

Calculate bedtime using sleep cycles

The simplest way to determine the optimal bedtime is to calculate backwards from the required wake-up time at intervals of 90 minutes, leaving about 15 minutes to fall asleep.

Example:

• Wake up time: 6:30am
• Sleep goal: 7.5 hours=5 cycles
• Sleep time: 15 minutes
• Best bedtime: 10:45 PM

Try Sleep Cycle Calculator for easy personalization.

How environment and habits affect sleep quality

Even if your bedtime is ideal on paper, certain lifestyle choices can delay or disrupt your sleep:

• The blue light emitted by the screen inhibits melatonin
• Consuming caffeine after 2pm can delay sleep time
• Late night dining or vigorous exercise can stimulate alertness
• Stress or impatient thoughts can hinder relaxation

Maintain good sleep hygiene - a dark, cool room; bedtime digital detoxification; a calm bedtime routine can help you fall asleep faster and maintain longer sleep.

Unveiling the myth of bedtime

Several misunderstandings about sleep time still exist:

• Myth: "As long as I sleep for 8 hours, I can go to bed at 2am"
  Reality: It disrupts your circadian rhythm and reduces sleep quality.
• Misconception: "I don't need to sleep. I sleep when I'm tired"
  Reality: Irregular sleep can disrupt your biological clock.
• Misunderstanding: "The earlier, the better"
  Reality: Bedtime should match your sleep needs and biological clock.

These issues are further explored in Common Sleep Misconceptions: Your Views on Good Sleep May Be Wrong.

Conclusion: Consistent with biology for better rest

The optimal bedtime is when the following conditions are met:

• Your natural melatonin rhythm
• Complete sleep cycle (multiples of 90 minutes)
• Your wake-up time and lifestyle

For most people, sleeping between 10 and 11 pm ensures optimal consistency with their physiology and sleep structure. But equally important is maintaining consistency - sleeping and waking up at the same time every day.

To establish an efficient daily rhythm based on your sleep pattern, please refer to How to Use a Sleep Cycle Calculator to Create an Efficient Work and Rest Schedule.

References

• Why is a 90 minute sleep cycle the most effective
• Best Sleep Time Guide for Different Age Groups
• Common Sleep Misconceptions: Your perception of good sleep may be incorrect
• Sleep Cycle Calculator
• The National Sleep Foundation. (2015). How much sleep do we really need? https://www.sleepfoundation.org
• Hirshkowitz, M. et al. (2015). Sleep Health, 1(1), 40-43. https://doi.org/10.1016/j.sleh.2014.12.010
• Walker, M. (2017). Why do we sleep. Scribner.
• Czeisler, C.A. (2013). Nature Magazine, 497(7450), S13. https://doi.org/10.1038/497S13a