As the name implies, the Thursday Council formally uses a different system of timekeeping. It isn't necessarily perfect (and doesn't aim to be), but is generally culturally neutral.

The Thursday week includes seven days, each called Thursday and numbered one to seven. The week begins on Thursday 1 and ends on Thursday 7. As per the specifications of decimal time, originally from the French Republican calendar used in France from 1794 to 1800, each day includes 10 hours. Each hour is 100 minutes, and each minute is 100 seconds. For parity with standard time, 0:00 aligns with UTC 00:00. Naturally, Thursday time does not include time zones, and the time is universal regardless of geographic location.

The calendar is based on Fixed Week Calendar (FWK; Fixierter Wochenkalender), a 13-month system that divides each month into exactly 28 days and four weeks. FWK is similar to the International Fixed Calendar, except each week begins with Monday per ISO 8601. The Thursday calendar differs in two ways: first, it uses the Thursday week, and second, it uses month names derived from toki pona vocabulary, as described by tokiponist soweli Kina. They proposed month names based on the history of Earth and the evolution of life, such that:

• mun Wan - the initial state of the universe
• mun Kon - the time after the big bang, when the universe was mostly gasses/plasma (kon) like hydrogen and helium
• mun Seli - the beginning of star formation
• mun Ma - the formation of the planet earth
• mun Telo - the formation of liquid water on earth
• mun Mama - refers to LUCA, the common ancestor of every living thing on earth
• mun Kasi - origin of plants
• mun Pipi - origin of arthropods
• mun Kala - origin of fish
• mun Akesi - origin of land tetrapods
• mun Waso - evolution of avian dinosaurs
• mun Soweli - evolution of mammals
• mun Namako - the development of culture

To cleanly align with the solar year, 13-month calendars typically include an extra day. In FWK, the this is simply called "year day," and it exists outside the typical week at the end of a year before a new one begins. It does not belong to a week or month. The other extra day, leap day, also does not belong to a week or month and sits between Sunday and Monday and the months of June and Sol, appended approximately every four years.

The Thursday calendar also includes these extra days. However, year day instead refers to the day which includes the moment of the UTC December solstice, defined as the precise instant when the Sun’s geocentric ecliptic longitude equals 270 degrees. Year day is a purely separational intercalary day: it does not belong to any year, is not counted in the 364 days of the year, is not a weekday, and is not included in a month. Therefore, a Thursday year can be defined as the 364 month-days immediately following a year day, occurring between the first moment (0:00:00 or 00:00 UTC) of mun Wan 1 and the last moment (9:99:99 or 23:59:59 UTC) of mun Namako 28. Additionally, leap day is also considered a separational intercalary day, not belonging to a year or counted as a weekday, but is only included if the quantity of UTC midnights elapsed between the first moments of two consecutive year days is 366. In such a case, the additional intercalary day is necessary, resulting in a total of 366 days in the solstice-to-solstice interval to match the 366 UTC midnights that passed. When a leap year is included, it falls between mun Mama and mun Kasi instead of FWK's June and Sol, and is not counted as part of any week or month.

Finally, the Thursday year 0 refers to the year which contains the Unix epoch moment. All times should dated relative to this epoch.

Other clarifications:

• A Thursday-day consists of the 100,000 seconds in the half-open interval of [0:00:00, 10:00:00), where 10:00:00 refers to the same second as the next day's 0:00:00. Similarly, year day is the date whose UTC interval [00:00, 24:00), equivalent to the Thursday-day interval, contains the solstice instant.
• Leap seconds do not exist in Thursday time. The typical UTC leap second notation of 23:59:60, which would correspond to 9:99:100, is an invalid timestamp. This aligns with the international decision to eliminate leap seconds from UTC by 2035.