In the Atlantean Union (AU), the official calendar is set by the ISO 8601 international standard. This standard requires date and times to represented in yyyy-mm-dd (but colloquially day, month, year) and 24-hour format (in writing with a colon or h as a separator, with minutes and seconds written with two digits and hours with a leading zero). The calendar used by the standard is the Common Era (CE) Gregorian calendar . However, there has been a push to reform the calendar to be more accurate and secular. Reformers propose the adoption of the Solar Khayyam (SK) calendar, which is based on the Iranian (Persian) Solar Hijri and French Republican calendars. This solar calendar is named after Persian poet, astronomer, philosopher and mathematician Omar Khayyam who led the solar calendar reform in 1079 CE . The combination of these two calendars in the Solar Khayyam calendar reflect the pursuit of harmonisation of Eastern and Western cultures in a secular and rational fashion.
Given the post-Enlightenment aspirations of decimalisation (see the decimalised franc currency and the Metric Calendar of Infernia, which is très Alphaville, Metropolis, and Dieselpunk) and metrication, there was a desire to decimalise the calendar like in the French Republican calendar, which had months divided into 30 days, weeks into 10 days, days into 10 decidays (decimal hours), hours into 100 millidays (decimal minutes), minutes into 100 quintodays (decimal seconds), whilst a year was still divided into 12 months. To the Pythagoreans, 10 was the perfect and complete number as it symbolised multiplicity originating from unity of one, human manual and pedal digits, and the spatial dimensions of linear, planar and material points (physical elements in a geometric ensemble with coordinates or parameters in a line, curve, plane, surface, vector, variety or space). However, this arrangement required five (or six in leap years) complementary days added at the end of months to approximate the tropical solar year. Likewise the Solar Khayyam calendar discards the duodecimal (base-12)—or tetravigesimal (base-24) in the case of the unambiguous 24-hour clock that combines two 12-hour periods with a.m. (ante meridiem) before and p.m. (post meridiem) after midday—and sexagesimal (base-60, which originates from the ancient Sumerians and Babylonians, who developed the arc degree, minute and second of an angle) time system. In decimal time, a quintoday is 0.864 (SI) seconds, a milliday 1.44 minutes, and a deciday 2.4 hours. The time can be written using: (1) a dd for deciday, md for milliday, and qd for quintoday as separators; (2) a colon as the separator; or (3) as a decimal day (d). Although Solar Khayyam calendar divides months into days differently, it divides the year into 12 months.
Moreover, instead of writing years in Roman numerals as is the case in the French Republican calendar, the Solar Khayyam calendar uses the Hindu–Arabic numeral system, which is preferable in spirit of decimalisation. Unlike the Gregorian calendar which begins the new year on 01 January, and like the Solar Hijri calendar, in the Solar Khayyam calendar the new year begins on the vernal (northward) equinox, when the Sun crosses 0° from south to north  as observed from the Galileo Observatory. The vernal equinox usually occurs on the 20 March or 21 March. The new year festival is called "New Day", symbolic of the awakening of life from the hibernation of winter. The holiday also celebrates Earth and Nature. The calendar uses astronomical calculation and computation for determining the vernal equinox so it has no intrinsic error. This feature makes it an observation based calendar and the most accurate solar calendar in contemporary use . This is similar to the more recent French Republican calendar which begins its new year on the autumnal (southward) equinox. Lastly, the proposed calendar does not implement daylight saving (summer) time.
The origin (year zero) of the current epoch (Holocene Era or HE) is defined to be the end of the Pleistocene and beginning of the Holocene epoch—the end of the last major glacial epoch or "ice age"—or 9701 BCE in the Gregorian calendar. This so-called "Anthropocene" epoch marks when humans transitioned from a chaser-collector lifestyle to agriculture and fixed habitation (i.e., human civilisation) in what is called the Neolithic Agricultural Revolution. Thus, the date of Tuesday, 20 February 1996 CE would be Second-day, 01 Pisces 11695 HE (11695-02-01, or the format yyyyy-mm-dd.ddmdqd where the day is a decimal day). Since there is a year zero (as a zero-based ordinal numbering system, which is parallel to the cardinal system that represents count rather than order), decades and centuries begin on years that are multiples of 10 and 100, respectively.
There are 12 months in a year in the Solar Khayyam calendar. The origin of 12 is that there are about 12 lunar cycles in a year (note that the Solar Khayyam calendar is not a lunar calendar; this is merely an artefact). The names of months correspond to the 12 signs of the tropical zodiac (formerly used in astronomy as an ecliptic celestial coordinate system, not to be confused with pseudoscientific astrology), where a sign corresponds to coordinates each occupying 30° of ecliptic (celestial) longitude. The number of days in a month vary since the length of seasons (three month quarters, with six months a semester) vary in length, with longer months clustered near aphelion (the apsis or point in the elliptical orbit where Earth is furthest from Sun, with the apogee the equivalent for terrestrial satellites) and shorter months clustered near perihelion (where Earth is closest to Sun) .
Following a septenary (base-7) numeral system (in reference to the seven candles of the candelabrum, and according to Robert Graves, in turn the planets or planetary spheres of antiquity), there are seven days in the week (septimane or hebdomad). Seven days is approximately a quarter of the lunar month . Each week has three rest days on the fifth, sixth, and seventh days. The working week is the first four days (begins on the first day and ends on the fourth day). The working day is regulated to 3.25dd, resulting in a maximum 13.00dd duration working week. Working hours are 03dd 75md 00qd (0.375d) to 07dd 50md 00qd (0.75d) with a 0.5dd duration break (interruption, pause, repose, hiatus, furlough or absence) for leisure. The days of the week are simply named as ordinal numbers, allowing for direct translation:
Given that a solar (tropical or more precisely the vernal-equinox) year fluctuates in length, the calendar year fluctuates between 365 or 366 days, depending on if it is a intercalary (leap) year . In a intercalary year a 30th day is added to the 12th month. A new day begins at (00dd 00md 00qd) and ends before (09dd 99md 99qd) midnight. Since the first day of the calendar year cannot start at the precise time of the vernal equinox but instead at midnight, if the vernal equinox occurs before midday (05dd 00md 00qd) then that day is the New Day, whereas if it occurs after midday then the New Day is the following day.
The intercalation system is relatively complex. It follows a 33-year intercalation cycle that consists of eight intercalary years of 366 days and 25 ordinary years of 365 days. The two kinds of intercalary years are quadrennial and and quinquennial, meaning they occur after three ordinary years and after four ordinary years, respectively. In the 33-year cycle, the first intercalary year is quinquennial (year 5) and the remaining seven are quadrennial (years 9, 13, 17, 21, 25, 29, and 33). Every 33 years and rarely after an interval of 29 years, between a quadrennial period, the vernal equinox occurs near midnight thereby creating a quinquennial period. This rarity occurs because the vernal equinox is tracked by observation.