Every sleep app offers a timer. Most don't explain what to set it to or why. Here's the underlying logic: the timer length matters more than people assume, and the right pick depends on what happens to you between minute 12 and minute 90.
How long sleep onset actually takes
The clinical term is "sleep onset latency" (SOL). For healthy adults the median is 10–20 minutes. People with insomnia run longer (often 30+ minutes). People with extreme exhaustion or sleep deprivation are sometimes asleep in under 5 minutes — that's actually a sign of sleep debt, not a good sleeper.
So for most readers, the audio is meant to cover the falling-asleep window. The question is what happens after you're asleep.
The four common timer presets, in order
15 minutes
Covers the falling-asleep window for most adults. If you fall asleep quickly (under 10 minutes) and don't have noise sensitivities, this is enough.
Failure mode: if you fall asleep in 10 minutes but wake at minute 20 because the apartment AC clicks on and the audio just stopped — the audio that was masking the click isn't there anymore. You're now awake at 11:25 PM with no masking. This is the single most common reason 15-minute timers underperform.
30 minutes
Covers a longer falling-asleep window plus a "consolidation buffer" — the first 10–15 minutes of sleep when arousal threshold is still relatively low. This is the default in most sleep apps and the right pick for most adults.
Failure mode: environmental noises peaking in the 30–90 minute window (upstairs neighbors arriving home, traffic spike, partner snoring) hit a now-quiet bedroom.
60 minutes
Covers the entire sleep-onset window plus the first sleep cycle (~90 minutes per cycle, so 60 mins gets you well into the first cycle including the first slow-wave segment). At minute 60 you're typically in deep slow-wave sleep — high arousal threshold, environmental noise less likely to wake you.
Best pick if: you live somewhere with predictable nighttime noise that fades after 11 PM but spikes briefly around midnight (urban areas with predictable patterns).
90 minutes
One full sleep cycle. You finish the first cycle in deep sleep with the audio still on, then the audio stops as you're naturally transitioning out of deep sleep — minimizing the chance the audio-cutoff itself wakes you.
Best pick if: the audio stopping has historically been what wakes you (you're sensitive to the absence of expected sound).
All night
Not a "timer" — just runs until you stop it. Best for noisy environments or for people who consistently wake at 3 AM and need continuous masking to fall back asleep.
Cost: phone battery + your device's display being on (or speaker draw). Sleep Sine's Apple TV mode is designed around this case — the TV plays through the night, the phone doesn't.
The "audio stopping woke me up" failure mode
Worth its own callout. If your bedroom has any masking sound — a fan, the AC, an apartment building's HVAC — your sleeping brain has adapted to that masking floor. When the sleep timer cuts off and the room goes from 45 dB (with audio + AC) to 35 dB (AC only), the 10 dB drop is itself a change event your brain can orient to. Some people wake at exactly that moment.
Two ways to avoid it: pick a timer length that ends during a natural sleep-stage transition (60 or 90 minutes), or let the audio fade out gradually rather than cut off (Sleep Sine fades audio over the last 30 seconds for exactly this reason — a slow fade is below the brain's change-detection threshold).
How to pick yours
- Start with 30 minutes. If sleep happens easily and you don't notice the audio stopping, you're done.
- Try 60 if you wake within the first hour. The longer timer covers more of the first sleep cycle.
- Try 90 if the audio stopping seems to be what wakes you. Cycle-aligned cutoff is gentler.
- Use all-night for environmental noise or 3 AM wakings. Continuous masking; no cutoff to react to.
What Sleep Sine does specifically
Sleep Sine offers 15 / 30 / 60 / 90 minute timers plus an indefinite "all night" mode. All timers include a 30-second soft fade on the last segment of audio — the audio doesn't cut, it gradually drops to silence. This is the cheapest and most-effective fix for the audio-stopping-woke-me-up problem.
On Apple TV, the indefinite mode runs through the night with the TV screen dimming but not sleeping — the scene plays continuously while consuming significantly less power than a typical TV in "on" state. See our guide on sleeping with an Apple TV ambient screen on for the details.