7.3. Datetime Standards

• Date and time formats varies from country to country [20]

7.3.1. Date

Formal date format in USA [27]

4/12/61         # short
April 12, 1961  # long

Formal date format in Japan [26]:

61/04/12        # short
1961年04月12日   # long

20/12/31        # short
平成20年12月31日  # long

Formal date format in Germany:

12.04.1961      # only

Date format in Poland:

12 kwietnia 1961
12 kwiecień 1961

12 IV 1961
12.IV.1961

12.4.1961
12.04.1961

12/4/1961
12/04/1961

12-04-1961
1961-04-12

Which format is a formal standard in Poland? There is no formal standard for date format in Poland. There is only a recommendation to write dates using ISO-8601 format (yyyy-mm-dd) [25]. However hardly anyone including government in official documents and forms is using it.

7.3.2. 12 and 24 Hour Clock

• What AM stands for?

• What PM stands for?

24 hour clock:

07:00       # morning
19:00       # evening

12 hour clock:

7:00 AM     # morning
7:00 PM     # evening

7.3.3. Noon and Midnight

• Confusion at noon and midnight [21]

• Which time is a midnight?

• Which time is a noon?

24 hour clock:

00:00
12:00

12 hour clock:

12:00 am
12:00 pm

7.3.4. Exactly Midnight

• 00:00:00.000000 - day start, exactly midnight

• 23:59:59.999999 - day end, excluding last microsecond

• 24:00:00.000000 - day end, including last microsecond

Day end, excluding last microsecond:

start = 2000-01-01 00:00:00.000000
  end = 2000-12-31 23:59:59.999999

Day end, including last microsecond:

start = 2000-01-01 00:00:00.000000
  end = 2000-12-31 24:00:00.000000

7.3.5. After Midnight

• Times after Midnight [22]

23:00 - 01:30
23:00 - 25:30

7.3.6. Leap Second

• International Earth Rotation and Reference Systems Service (IERS)

• UTC leap second [18]

• Leap second discontinuation post 2035 [1]

• Issues created by insertion (or removal) of leap seconds

• Calculation of time differences and sequence of events

• Missing leap seconds announcement

• Implementation differences

• Textual representation of the leap second

• Binary representation of the leap second

• Other reported software problems associated with the leap second

• June 30th or December 31st

• Introduced in 1972

• Last leap second (to date) was in 2016

International Earth Rotation and Reference Systems Service (IERS) is the standards keeping body established that there was not enough difference between time as measured based on atomic clocks (UTC) and time as measured by the Earth's natural rotation (UT1) to warrant making a ripple in time. UT1 varies thanks to phenomena like gravitational interactions with the Moon and Sun, and geological activities such as earthquakes which alter the speed of Earth's rotation. UTC and UT1 therefore might not always match. The IERS maintains a maximum value of ±0.9 seconds by which the two can vary. If that limit is exceeded, various applications that sync UTC and UT1 can strike trouble as time stamps don't align. That's when a leap second is thrown in. [18]

Earth's rotation slowed in recent decades, creating a need for 27 leap seconds introduced between 1972 and 2016. Our planet's spin has sped up a little since – which is why we've not had a leap second added for a few years. Leap seconds are added to UTC time at the end of December or June, and announced six months before their implementation. [18]

While a leap second has never been subtracted, doing so is a theoretical possibility and may one day be warranted. [18]

Leap seconds are more than timekeeping trivia – computers must keep up with very precise changes to the way humanity measures time. Last time a leap second was added, Cloudflare suffered a limited service interruption and Linux servers choked. Systems that rely on precise timing – such as GPS and financial trading platforms – can be affected too. Meta's engineering team therefore proposed doing away with leap seconds back in 2022. But adding leap seconds is a known problem, even if annoying and resource-sucking. As at least one blogger has noted: "No one, or almost no one, is ready for a negative leap second." [18]

Back in November 2022 The Bureau International des Poids et Mesures (BIPM) declared 2035 as the year in which the concept will be binned. The plan is to replace it with a "new maximum value for the difference (UT1-UTC) that will ensure the continuity of UTC for at least a century [18].

Normal second:

23:59:59
00:00:00

Leap Second:

23:59:59
23:59:60
00:00:00

Table 7.1. Leap Seconds since 1972

Year	30 Jun	31 Dec
1972	1	1
1973	0	1
1974	0	1
1975	0	1
1976	0	1
1977	0	1
1978	0	1
1979	0	1
1980	0	0
1981	1	0
1982	1	0
1983	1	0
1984	0	0
1985	1	0
1986	0	0
1987	0	1
1988	0	0
1989	0	1
1990	0	1
1991	0	0
1992	1	0
1993	1	0
1994	1	0
1995	0	1
1996	0	0
1997	1	0
1998	0	1
1999	0	0
2000	0	0
2001	0	0
2002	0	0
2003	0	0
2004	0	0
2005	0	1
2006	0	0
2007	0	0
2008	0	1
2009	0	0
2010	0	0
2011	0	0
2012	1	0
2013	0	0
2014	0	0
2015	1	0
2016	0	1
2017	0	0
2018	0	0
2019	0	0
2020	0	0
2021	0	0
2022	0	0
2023	0	0
2024	0	?
Total	11	16
27

7.3.7. Zero Padded

• Zero padded minutes, seconds and microseconds but not hours

• Variable length microseconds

Hours:

06:07               # ok
6:07                # ok

Minutes:

06:07               # ok
06:7                # error

Seconds:

06:07:00            # ok
06:07:0             # error
06:07:              # error
06:07               # ok

Microseconds:

06:07:00.000000     # ok
06:07:00.00000      # ok
06:07:00.0000       # ok
06:07:00.000        # ok
06:07:00.00         # ok
06:07:00.0          # ok
06:07:00            # ok

Microseconds:

06:07:00.000001     # different time, different length
06:07:00.00001      # different time, different length
06:07:00.0001       # different time, different length
06:07:00.001        # different time, different length
06:07:00.01         # different time, different length
06:07:00.1          # different time, different length

06:07:00.000001     # different time, same length
06:07:00.000010     # different time, same length
06:07:00.000100     # different time, same length
06:07:00.001000     # different time, same length
06:07:00.010000     # different time, same length
06:07:00.100000     # different time, same length

06:07:00.100000     # same time, different length
06:07:00.10000      # same time, different length
06:07:00.1000       # same time, different length
06:07:00.100        # same time, different length
06:07:00.10         # same time, different length
06:07:00.1          # same time, different length

7.3.8. Roman Numerals

• In latin V is read as U

• In latin I is read as J

• In latin IV is read as JU

• JU stands for Jupyter - roman god

• Louis XIV did not like IV and changed to IIII [28]

• There is a symetry in groups of four I, II, III, IIII, V, VI, VII, VIII, IX, X, XI, XII

IV
IIII

There is a symetry in groups of four:

I,   II,  III,  IIII    # Group with I and I
V,   VI,  VII,  VIII    # Group with V and I
IX,  X,   XI,   XII     # Group with X and I

In latin V is read as U, I is read as J, therefore IV is read as JU which stands for Jupyter - roman god.

7.3.9. Calendars

• Julian Calendar [8]

• Gregorian Calendar [3]

• Introduced by Pope Gregory XIII in October 1582

• Saudi Arabia was the last country to adopt Gregorian calendar in 2016

• There are only four countries which have not adopted the Gregorian calendar: Ethiopia (Ethiopian calendar), Nepal (Vikram Samvat and Nepal Sambat), Iran and Afghanistan (Solar Hijri calendar)

• List of adoption dates of the Gregorian calendar by country [2]

Table 7.2. Brief summary of adoption dates of the Gregorian calendar per country [2]

Year	Country/-ies/Areas
1582	Spain, Portugal, France, Polish-Lithuanian Commonwealth, Italy, Catholic Low Countries, Luxembourg, and colonies thereof
1584	Kingdom of Bohemia, some Catholic Swiss cantons
1610	Prussia
1648	Alsace
1682	Strasbourg
1700	Protestant Low Countries, Norway, Denmark, some Protestant Swiss cantons
1752	Great Britain, Ireland, and the 'First' British Empire (1707–1783)
1753	Sweden and Finland
1873	Japan
1875	Egypt
1896	Korea
1912	China, Albania
1915	Latvia, Lithuania
1916	Bulgaria
1917	Ottoman Empire
1918	Ukraine, Russia, Estonia
1919	Romania, Yugoslavia
1923	Greece
1926	Turkey (common era years; Gregorian dates in use since 1917 Ottoman adoption)
2016	Saudi Arabia

7.3.10. Astronomy

• Synodic day - the period for a celestial object to rotate once in relation to the star it is orbiting [10]

• Solar time - calculation of the passage of time based on the position of the Sun in the sky [9]

• Epoch (astronomy) [5]

• Sidereal Time [4]

• JD - Julian Day [6]

7.3.11. Databases

• SQLite dates and time are stored as TEXT, INTEGER or REAL values.

• TEXT as ISO-8601 strings ('YYYY-MM-DDTHH:MM:SS.SSS').

• INTEGER as timestamp, the number of seconds since 1970-01-01 00:00:00 UTC.

• REAL as Julian day numbers, the number of days since noon in Greenwich on November 24, 4714 B.C. according to the Gregorian calendar.

Applications can chose to store dates and times in any of these formats and freely convert between formats using the built-in date and time functions.

7.3.12. Space Industry

• UTC - Coordinated Universal Time [13]

• GMT - Greenwich Mean Time [11]

• MET - Mission Elapsed Time

• Relativistic effects

• Time dilatation due to speed approaching speed of light

7.3.13. Planet Mars

• MSD - Mars Sol Date [15]

• MTC - Coordinated Mars Time [16]

• Timekeeping on Mars [14]

• Mars Clock [12]

• Martian sidereal day is 24 h 37 m 22.663 s (88,642.663 seconds)

• Martian solar day is 24 h 39 m 35.244 s (88,775.244 seconds)

7.3.14. Military Time

• Military time [23]

• Military time zones [24]

• 24 hour clock

7.3.15. Decimal Time

• Unix time gives date and time as the number of seconds since January 1, 1970

• Microsoft's FILETIME as multiples of 100ns since January 1, 1601 [17]

• VAX/VMS uses the number of 100ns since November 17, 1858 [17]

• RISC OS the number of centiseconds since January 1, 1900 [17]

7.3.16. Other

• Swatch Internet Time - Beats @300 [7]

• sidereal day on Earth is approximately 86164.0905 seconds (23 h 56 min 4.0905 s or 23.9344696 h)

7.3.17. References

[1]

Gibney, E. The leap second's time is up: world votes to stop pausing clocks. Year: 2022. Retrieved: 2022-11-18. URL: https://www.nature.com/articles/d41586-022-03783-5 DOI: https://doi.org/10.1038/d41586-022-03783-5

[2] (1,2)

Wikipedia. List of adoption dates of the Gregorian calendar by country. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/List_of_adoption_dates_of_the_Gregorian_calendar_by_country

[3]

Wikipedia. Gregorian Calendar. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Gregorian_calendar

[4]

Wikipedia. Sidereal Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Sidereal_time

[5]

Wikipedia. Epoch Astronomy. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Epoch_(astronomy)

[6]

Wikipedia. Julian Day. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Julian_day

[7]

Wikipedia. Swatch Internet Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Swatch_Internet_Time

[8]

Wikipedia. Julian Calendar. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Julian_calendar

[9]

Wikipedia. Solar Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Solar_time

[10]

Wikipedia. Synodic Day. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Synodic_day

[11]

Wikipedia. Greenwich Mean Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Greenwich_Mean_Time

[12]

Wikipedia. Mars Clock. Year: 2022. Retrieved: 2022-05-10. URL: https://marsclock.com/

[13]

Wikipedia. Coordinated Universal Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Coordinated_Universal_Time

[14]

Wikipedia. Timekeeping On Mars. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Timekeeping_on_Mars

[15]

Wikipedia. Timekeeping On Mars - Mars Sol Date. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Timekeeping_on_Mars#Mars_Sol_Date

[16]

Wikipedia. Timekeeping On Mars - Coordinated Mars Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Timekeeping_on_Mars#Coordinated_Mars_Time

[17] (1,2,3)

Wikipedia. Metric time. Leap Second. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Metric_time

[18] (1,2,3,4,5,6)

Wikipedia. Leap Second. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Leap_second

[19]

Dobberstein, Laura. Time Lords decree: No leap second needed in 2024. The Register. Year: 2024. Retrieved: 2024-07-05. URL: https://www.theregister.com/2024/07/05/iers_decrees_no_leap_second/

[20]

Wikipedia. Date Time Formats. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/Date_format_by_country

[21]

Wikipedia. Noon Midnight. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/12-hour_clock#Confusion_at_noon_and_midnight

[22]

Wikipedia. Times After 2400. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/24-hour_clock#Times_after_24:00

[23]

Wikipedia. Military Time. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/24-hour_clock#Military_time

[24]

Wikipedia. Military Timezones. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/List_of_military_time_zones

[25]

Wikipedia. ISO8601. Year: 2022. Retrieved: 2022-05-10. URL: https://en.wikipedia.org/wiki/ISO_8601

[26]

Date and time notation in Japan. Wikipedia. Year: 2022. Retrieved: 2019-06-27. URL: https://en.wikipedia.org/wiki/Date_and_time_notation_in_Japan#Date

[27]

Date and time notation in the United States. Wikipedia. Year: 2022. Retrieved: 2019-06-27. URL: https://en.wikipedia.org/wiki/Date_and_time_notation_in_the_United_States

[28]

Why Do Watches Use the Roman Numeral IIII Instead of IV? Year: 2021. Retrieved: 2023-11-16. URL: https://www.watchmaster.com/en/journal/stories-en/roman-numeral-iiii-on-watches