Cycle

Cycles refer to a measure of time used in a variety of cultures. The exact nomenclature consists of 6 numbers, whose significance is currently not understood. The term cycle likely refers to a year, although the definition of the length of a year may vary by planet.

Usage
The usage of the cycle system seems to agree among the Galactic Federation and the Space Pirates. It has been suggested that a datecycle (term used by Captain Exeter) begins with government actions on a planet. For example, Zebesian datecycle could begin when the Pirates attempted to control of Zebes, and their base was overrun before 09.992.3 (see below). Tallon IV was the first known discovery of Phazon, on the Zebesian datecycle 10.229.2.

However, the datecycle varies by planet or system. Aether's phazon is discovered 4 cycles before 04.468.1 (Aetherian), suggesting 00.000.1 was the discovery of Aetherian Phazon.

Nomenclature
There are a variety of theories as to how the datecycle is read. One theory is the the first two digits denote the year, the next three the day of the year, and the final digit denotes time of day. However, the timespan from Metroid to Metroid Prime is three years (although how year is defined is unknown). However, the Aetherian calendar is on 07.159.9 at the opening of Metroid Prime 2. Given the fact Phazon hasn't been discovered for even 2 years as of Metroid Prime 2, and that the Pirate's exploration begins 7 cycles ago, it would seem inreconciliable that years refer to the first two digits.

However, the years could refer to the individual's planet's cycle year. If a planet has a shorter cycle orbiting a sun, its datecycle would increase faster. With these separate measurements of a "year", the dates are reconcilable. If Aether had very short cycles, it could have well been 7 Aetherian years within the span of 2 standard years.

Metroid Prime

 * The Space Pirate Logs (beginning at an unknown point after the "Fall of Zebes" date from 09.992.3-11.664.2
 * The span from Metroid to Metroid Prime is three years (definition of year unclear).

Metroid Prime 2

 * The Space Pirate Logs are dated 04.468.1-07.159.9.
 * Captain Exeter's report (shortly after planetfall) is dated 07.014.2, coinciding with the Pirate Log dates.
 * U-Mos is referred to as cycles old, supporting the theory that a cycle is a year.