Bedtime Window: When Your Body Most Wants to Sleep

Many people assume there's one bedtime that's best for everyone, like "you must be asleep before 10 pm." But sleep science gives a more personal answer: the bedtime that suits you depends on your own biological rhythm, not a universal clock time.

The Rhythm Window: Your Body Clock Decides

Everyone has an internal circadian rhythm that determines when the body starts "preparing for sleep": lowering core temperature, releasing melatonin, slowing metabolism. This timing varies from person to person. Some are naturally early (morning types), some naturally late (evening types). This is called your chronotype.

Based on your actual sleep data, Mellows estimates your current rhythm window: a time band reflecting your true biological rhythm. It honestly shows when your body currently tends to fall asleep, without forcing you into a socially "correct" schedule.

Why Mellows Doesn't Just Tell You the "Best Time"

Because "best" is a value judgment, and the app has no right to make it for you. Your biological rhythm is objective reality; your target schedule is subjective intent, and the two may differ. What Mellows does is show you both at once:

• Rhythm window: the phase your body is actually in right now (reality)
• Target window: when you'd like to fall asleep (intent)

The gap between them is yours to decide whether to close. If you want to sleep earlier, that gap is the direction to adjust toward gradually, not an order from the app about when to lie down.

Allow Some Flexibility in Bedtime

Chasing a to-the-minute bedtime every night is neither realistic nor necessary. Research shows that keeping your bedtime drift within about plus or minus 30 minutes (a total span of roughly an hour) already counts as "high regularity," enough to keep the body clock running steadily. So the window is a band, not a line.

What truly harms your rhythm is large drift: grinding through the workweek, then sleeping until noon on weekends. This "social jetlag" keeps the body clock misaligned and is linked to metabolic and mood issues.

How to Live With Your Window

Work with it, not against it: if you're a natural evening type, rather than forcing a 10 pm bedtime and staring at the ceiling, fall asleep within your rhythm window and protect your duration and regularity. Use light to shift it: bright morning light pulls your rhythm earlier; dimming lights and cutting screens at night keeps it from drifting later. This moves your body clock more effectively than simply "going to bed earlier." Stabilize first, then shift: if you want an earlier bedtime, move it up 15 minutes every few days so your rhythm can follow, which succeeds more often than jumping an hour at once.