Nap research is unusually specific about duration. A widely cited Sleep Research Society study found 10-minute naps were the most effective length for improving subjective sleepiness and cognitive performance.

The reason short naps work so well comes down to sleep inertia — the groggy, disoriented feeling you get waking from deeper sleep stages. Naps around the 45-minute mark are the awkward middle ground: long enough that you're likely to drop into slow-wave (deep) sleep, but not long enough to complete a full cycle.

Timing matters as much as length. Napping in the early afternoon, roughly between 1pm and 3pm, aligns with a natural dip in alertness most people experience regardless of how much sleep they got the night before.

Further reading: The science behind power naps (Harvard Health).