Lunch break, train platform, the gap before a meeting. Four of these five are old enough to be public domain in the US, so a free and legitimate full text is thirty seconds away on a volunteer archive like Project Gutenberg or Standard Ebooks.
The Lottery ≈10 min
Shirley Jackson · 1948 · in print; find it in her collections
The detail that does the damage is the black box: splintered, faded, shabby from decades of use, and nobody will replace it because replacing it would mean admitting there is a choice. Jackson spends her first half building a village fête and the second half taking it apart, and the final page rearranges everything you read before it. Still in copyright, so a library collection or a licensed ebook rather than a free archive.
The Story of an Hour ≈8 min
Kate Chopin · 1894 · public domain in the US
Louise Mallard is told her husband has died in a rail accident, goes upstairs alone, and sits at an open window watching the tops of trees while she works out — slowly, and against her own will — that what she feels is not grief. She repeats one word to herself under her breath, and Chopin lets the room fill with it. The closing sentence is one of the most efficient acts of cruelty in American fiction. Shortest thing on this page, and the best place to start if you have not finished a book in a year.
The Cask of Amontillado ≈12 min
Edgar Allan Poe · 1846 · public domain in the US
Montresor walks a drunk rival down into the family catacombs during carnival, on the promise of a rare sherry. What makes it work is the trowel he produces from under his cloak, a joke Fortunato does not get and the reader already does, plus the bells on the fool's cap still faintly jingling in the dark long after everything else has stopped. Poe never tells you what the insult was, and readers have argued about it ever since.
Hills Like White Elephants ≈10 min
Ernest Hemingway · 1927 · public domain in the US (pre-1929 publication)
A couple wait for a train at a Spanish station and talk around a decision. The word "operation" is said once. Nothing else in the story is named directly, and yet the argument is fully legible: Hemingway hands you two people's dialogue, the luggage with labels from every hotel they have slept in, and the hills across the valley the woman keeps looking at, and lets you assemble the rest. If you want to see what "iceberg theory" actually means in practice rather than in a lecture, it is ten minutes.
The Library of Babel ≈15 min
Jorge Luis Borges · 1941 · in print in translated collections
The universe is a library of identical hexagonal galleries holding every possible book: every arrangement of letters, so every true book, every false one, and oceans of gibberish between them. Borges then works through what living there does to people, including the sects, the purges, and the suicides down the ventilation shafts. It is closer to a proof than a story, and it sits in your head for weeks.