The current set of time in the Ninja Academy universe is Aetas Argentums, or AA. The planetary cycles are for all intents and purposes identical to Earth's - thus it is a 365-day Gregorian year (it's still called a Gregorian year, and let's not address the subject of why so we don't have to invent a Pope Gregory analogue). What happened 2100-ish years ago? The current dynasty of emperors came to power.
Before Aetas Argentum came, obviously, Aetas Aurum, which is abbreviated as AU, because it would be confusing to have two identical abbreviations for the same age. Note that Aetas Aurum also increases toward the current day - before Aetas Aurum the time used is unknown, but it is now referred to as Aetas Somnium, or sometimes Aetas Fabulus. Aetas Fabulus decreased approaching 0 AU.
The year is not like our normal year in which the seasons start and end. The New Year represents the first day of spring, followed by summer, fall and winter in that order. The last day of winter is also the last day of the year.
The timeline looks something like this:
| 1655; Fall | - | Rikudou Sennin forges 'ninjutsu', thus creating the ninja world. | -- |
| 1912; Summer | - | Konohagakure no Sato is formed. | -- |
| 1913; Spring | - | Kirigakure no Sato, Sunagakure no Sato and Kumogakure no Sato are formed. | -- |
| 1913; Summer | - | Kusagakure no Sato and Iwagakure no Sato are formed. | -- |
| 1916; Winter | - | Yukigakure no Sato is formed. | -- |
| 1921; Spring | - | Amegakure no Sato is formed. | -- |
| 1952; Winter | - | Konoha and Iwa go to war. | -- |
| 1955; Fall | - | Namikaze Minato decimates one half of Iwa's forces. Iwa forced to surrender to Konoha. | -- |
| 1960; Summer | - | Namikaze Minato is elected Yondaime Hokage of Konoha. | -- |
| 1960; Fall | - | Kyuubi attacks Konoha, Namikaze Minato is killed by sealing the beast. Birth of Uzumaki Naruto. | -- |
| 1962; Summer | - | Otogakure no Sato is formed. | -- |
| 1966; Fall | - | The Uchiha Clan is thoroughly wiped out under questionable circumstances. | -- |
| 1976; Fall | - | Konohagakure no Sato is destroyed by the hands of Pain/Nagato under the cover of the organization Akatsuki. | -- |
2102; Spring |
- | Ninja Academy Role Play Begins | |
| 2104; Fall | - | Iwagakure no Sato is invaded and controlled by a group by the name of "Akatsuki", relation to the historical Akatsuki unconfirmed. | -- |
| 2105; Summer | - | Iwagakure no Sato is freed of "Akatsuki" rule. | -- |
| 2106; Summer | - | International Chuunin Exams in Kusagakure no Sato. | -- |
| 2107; Spring | - | The known world is invaded and conquered by the Kumogakure Empire in the most successful blitzkrieg attack known to history. | -- |
| 2107; Spring | - | Kyoukage, Tomoshibi Mikomi, is killed in combat against Kumogakure no Sato. | -- |
| 2107; Summer | - | The Ninja Crime Investigation Agency (NCIA) is formed within the Kumogakure Empire. | -- |
2107; Summer to 2109; Spring |
- | Two Year Time Skip in Role Play | |
| 2109; Spring | - | Otogakure no Sato fails in an attempt to free itself from the Empire; remaining resistance members are disbanded to other countries. | -- |
| 2109; Summer | - | Iwagakure no Sato is freed from the Empire. | -- |
| 2109; Summer | - | Konohagakure no Sato fails in an attempt to free itself from the Empire; remaining resistance members are disbanded to other countries. | -- |
| 2109; Fall | - | Iwagakure no Sato is invaded by Yukigakure no Sato. Tsuchikage Hikado is killed by "Uchiha Madara", the invasion is unsuccessful. | -- |
| 2109; Winter | - | Fang's NCIA Hunting Squad has vanished. Members scattered through different parts of the world. | -- |
| 2109; Winter | - | Gobi 'frees' Kusagakure no Sato from the Empire. | -- |
| 2109; Winter | - | Sunagakure no Sato is freed from the Empire. | -- |
| 2110; New Year | - | Kirigakure no Sato is freed from the Empire. | -- |
| 2110; Spring | - | Battle of Nigiyakashufu resulting in the fall of the Kumogakure Empire and the NCIA. Death of Raikage, Inabikari Raikou. | -- |
| 2110; Spring | - | The Momochi Rakurai Explosion, a nuclear detonation, takes place in the Northern Sea during the battle of Nigiyakashufu. | [?] |
| 2110; Spring | - | Otogakure no Sato is freed from remaining NCIA rule. Death of Urseial Li. | -- |
| 2110; Spring | - | Kirigakure no Sato's GERT exams take place. | -- |
| 2110; Summer | - | Iwagakure Air Federation is founded. | -- |
2110; Summer |
- | Five Year Time Skip in Role Play Begins | |
| 2113; Fall | - | Tsuchi Yuki Border Agreement of 2113 is signed by Earth and Snow Countries. | [?] |
| 2114; Spring | - | The Western Earth Invasion happens in the Country of Earth. | [?] |
| 2114; Fall | - | Tsuchi Yuki Aggression Declaration is made by the leaders of the Country of Earth. | [?] |
2115; Summer |
- | Five Year Time Skip in Role Play Ends | |
| 2115; Summer | - | Kirigakure Civil War. | -- |
| 2115; Fall | - | Internation Chuunin Exams in Metropolis | -- |