The Circadian Answer
Your body produces melatonin on a predictable schedule driven by your circadian clock. For most adults (intermediate chronotypes), melatonin begins rising around 9–10 PM, peaks between midnight and 2 AM, and declines sharply in the morning. Going to bed when melatonin is rising — rather than fighting it or waiting hours past its peak — produces the fastest sleep onset and deepest early-night slow-wave sleep.
Early chronotypes (larks) have melatonin rising at 8–9 PM. Late chronotypes (owls) don't see it until 11 PM–1 AM. The "best time to sleep" is genuinely different for these groups — and forcing an owl to sleep at 10 PM produces the same insomnia as forcing a lark to stay up until midnight.
The Cycle-Aligned Answer
Beyond chronotype, the best time to sleep is the time that allows your alarm to fire at the end of a complete 90-minute cycle. For a 7 AM alarm, this means bedtimes of 11:15 PM (5 cycles) or 9:45 PM (6 cycles). A chronotype-aligned bedtime that also hits cycle boundaries is the optimal combination.
What the Research Shows
Large population studies consistently find that adults going to bed between 10 PM and midnight have the best health outcomes, independent of total sleep duration. This window is not arbitrary — it aligns with the natural melatonin peak for most adults and captures the most restorative early-night deep sleep in the first 2–3 cycles.
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