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The 28-hour day is a semi-serious concept of personal time management where an organization or individual lives by a 28-hour long schedule with exactly six such cycles within a standard 7-day week of 168 hours, since 6 × 28 = 7 × 24. It was made popular in an issue of the XKCD comic by Randall Munroe.

This schedule will eventually drive you mad.

The plan suggests a sleep cycle of 19 to 20 hours awake followed by 8 to 9 hours asleep: 20/8 or 19/9.

For people who do not need more but less hours per sleeping cycle, the 21-hour day would be an alternative with eight cycles per week since 8 × 21 = 168 as well.

Overview of 21-, 24- and 28-hour days within a standard week
Weekday Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Hour 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Nominal light darkness daylight darkness daylight darkness daylight darkness daylight darkness daylight darkness daylight darkness daylight darkness
16:8 asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep
20:8 awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake
19:9 awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake
15:6 awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake asleep awake

See also[]

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