Nap Timer

<p><strong>Why this helps:</strong> A 2016 study in Sleep (PMC) found that a 10-minute nap produced little to no sleep inertia, while a 30-minute nap was associated with grogginess on waking, because by roughly 30 minutes the brain drifts into deeper (slow-wave) sleep that is hard to wake from cleanly. A 2023 reanalysis in Scientific Reports found a 90-minute nap lets a sleeper complete a full cycle and wake from lighter sleep, limiting inertia to a brief period. WHOOP's 2024 summary of the nap literature frames the 10-20 minute window as the "power nap" zone (light sleep, quick alertness) and 90 minutes as the "full cycle" option.</p><h4>Screen — Nap timer home</h4><p><strong>Header:</strong> How long do you have?</p><p><strong>Subhead:</strong> Pick a length that ends in light sleep, so you wake clear instead of groggy.</p><p><strong>Preset 1</strong></p><ul><li><strong>Label:</strong> Power nap</li><li><strong>Duration:</strong> 10 minutes</li><li><strong>One-line:</strong> Just enough to lift the fog. You stay in light sleep, so there's no grogginess on the other side.</li></ul><p><strong>Preset 2</strong></p><ul><li><strong>Label:</strong> Recharge nap</li><li><strong>Duration:</strong> 20 minutes</li><li><strong>One-line:</strong> A little deeper rest, still in light sleep. Sharper focus and energy without crossing into the heavy stuff.</li></ul><p><strong>Preset 3</strong></p><ul><li><strong>Label:</strong> Full cycle</li><li><strong>Duration:</strong> 90 minutes</li><li><strong>One-line:</strong> One complete sleep cycle, ending where it's light again. Best when you're truly behind on sleep and have the time.</li></ul><p><strong>Helper line (below presets):</strong> Avoid the 30-to-60 minute range. That's where you wake mid-deep-sleep and feel worse than when you started.</p><p><strong>Custom option:</strong> Set your own (with inline warning if user picks 30-60 min: "Heads up: waking in this window often brings grogginess. 20 or 90 minutes usually feels better.")</p><p><strong>Primary button:</strong> Start nap</p><h4>Screen — Nap in progress</h4><p><strong>Header:</strong> Resting.<br><strong>Body line:</strong> Wake-up in {countdown}. Let go. We'll bring you back gently.<br><strong>Subtle line:</strong> Set the phone down. Close your eyes. Nothing to watch.<br><strong>Secondary button:</strong> End nap early</p><h4>Screen — Wake-up</h4><p><strong>Header:</strong> Time to come back.<br><strong>Body:</strong> Take a slow breath. Stretch. Give yourself a minute before you stand. You napped for {duration}.<br><strong>Tip line (10/20 min):</strong> You stayed in light sleep, so you should feel clear within a minute or two.<br><strong>Tip line (90 min):</strong> You finished a full cycle. A little fuzziness is normal and will pass quickly.<br><strong>Primary button:</strong> I'm up</p><h4>Research note (shown via "Why these lengths?" link)</h4><p>The presets aren't arbitrary. Sleep moves in stages, from light to deep and back again, over roughly a 90-minute cycle. How you feel when you wake depends almost entirely on which stage you wake from.</p><p>Ten and twenty minutes keep you in light sleep (stages 1 and 2). You get the alertness boost without the grogginess. A 2016 study in Sleep found a 10-minute nap produced almost no sleep inertia, while a 30-minute nap left people groggy, because by then the brain has slipped into deeper sleep.</p><p>Ninety minutes is the other safe choice. It lets you travel all the way through a full cycle, including deep sleep and REM, and come back out to light sleep before the alarm. A 2023 reanalysis in Scientific Reports found a 90-minute nap limits grogginess to a brief moment because you wake from a lighter stage.</p><p>The danger zone is roughly 30 to 60 minutes. That's long enough to fall into deep sleep but too short to climb back out, so the alarm catches you at the worst moment. That's the grogginess called sleep inertia. Pick 10, 20, or 90, and you sidestep it.</p><h2>Sources</h2><ul><li>Hilditch et al., Sleep / PMC, 2016 — 10-minute nap produced minimal sleep inertia; 30-minute nap associated with grogginess.</li><li>Scientific Reports, 2023 reanalysis — 90-minute (full-cycle) nap limits sleep inertia to a brief period by ending in lighter sleep.</li><li>WHOOP, "Best Nap Length," 2024 — 10-20 minute "power nap" window (light sleep) vs 90-minute full-cycle option.</li></ul>