The measurement and expression of time in Eorzea, like the real world, is governed by a fundamental set of rules. The Dusty Tomes found in various guilds explain these standards in a book called The Five Ages - An Eorzean Chronology, albeit in heavily archaic language. In-game, time can be expressed in either a 24-hour clock format, or a 12-hour format with a.m./p.m. You can also change the clock to be Eorzea Time (ET), System Time (ST) of the server you're on, or Local Time (LT) showing your current real-life time. There is also an icon showing the current weather for the zone you're in, in the upper-right corner of the mini-map.
Eorzean Time Units and Conversions
|Eorzean Increments||Components in Eorzean Units||Conversion into Earth Time|
|1 minute||60 seconds||2 11/12 seconds|
|1 bell||60 minutes||2 minutes, 55 seconds|
|1 sun||24 hours||70 minutes|
|1 week||8 days||9 hours, 20 minutes|
|1 moon||32 days||37 hours, 20 minutes|
|1 year||12 months||18 days, 16 hours|
Each month begins with a new moon, and each phase lasts 4 Eorzean days. Currently the moon phase of the moon shown in the Eorzea sky at night seems random and rarely matches the phase icon. Also, it is unknown at this time what influence, if any, the moon phase has on in-game activities.
See also: The Five Ages - An Eorzean Chronology
The polarities have been a source of confusion in the lore; the months of the year are divided so that each of the six elements is represented by an astral and umbral month, totaling 12 months in a year. However, actions that were based in astral or umbral energy clearly identified three elements associated with each, with the three elements at the top of the wheel (wind, lightning, and fire) representing "the astral heavens above" and the three at the bottom (water, ice, and earth) representing "the umbral depths below." Not only do these two things seemingly contradict eachother philosophically, but these actions have since been changed to identify astral and umbral energy as "neutral," so it is unknown if these associations even still exist or carry any influence.
This is the term Eorzeans use to describe a day, being a "period which lasts for the duration of four cycles of the six elemental hours." It is stated that there are two astral cycles and two umbral cycles, and it is assumed that polarity association alternates (as the years do) from one cycle to the next. These hours are frequently referred to as "bells" by NPCs.
Even though each bell is associated with an element and polarity, each only lasts just short of three Earth minutes, so even if it did have some influence in-game, it would be very difficult to take advantage of it.
This is the term Eorzeans use to describe a month, which "spans four cycles of eight Suns, and is thus the sum of thirty and two." Unlike real-world months, a moon's weeks are of equal length, representing the six elements and both polarities. The new moon phase fittingly falls on the first day of each moon. Throughout the month, the moon waxes to its peak, which occurs on the 17th, and wanes back down to the next new moon, which begins the next month. Again, it is unknown at this time if the daily element associations or moon phases have any impact at all, or if they are purely lore-based.
A year, to Eorzean culture, "can be said to be the length of twelve Moons." Each of the six elements is associated with two successive months, the first being the astral month of that element, and the second the umbral. For instance, "the first and second Moons of the Year are the first astral and first Umbral and together they share affinity with Ice." This can get confusing, because a month with the name, "the third astral moon" is actually the fifth month of the overall year. This chart can be used for easy reference.
To articulate a singular date of any given year, begin with the numerical day expressed as one of the thirty-two suns in a moon, followed by the name of that month. For instance, the in-game widget's date of 10/17 would be expressed as "the seventeenth sun of the fifth umbral moon."
Eorzea does not express years in clusters of ten, as does the real-world with decades, but in clusters of twelve. Each year in a cluster is associated with one of The Twelve.