This isn't that easy topic because the infos lying all over the place in those works I mentioned ITT. And these books and articles have many holes and conflicting statements. Still I'll try to give a summary.
I also have no idea what kind of pictures I should upload as illustrations.

The whole lifetime of Ynev is divided into nine Eras, one Era supposed to be 3-5 thousands years long but it's blurry. Different cultures have different chronology, human cultures have at least five or six, other races probably has their own. The authors and fans use mostly the Pyar calendar and Pyar chronology when they give the date for a certain events. This chronology is based on the foundation of a city, called Pyarron, this marks the year 0. The game's present is somewhere about the years 3690-3700 of Pyarron which also marks the end of the Seventh era. When does it start? No idea, I would guess somewhere around the year 500 before Pyarron.
In the following I will rarely give precise dates for anything.