Callenders are a complex subject, as time moves at different rates throughout the Multi-Verse. Generally, pinpointing a specific date and time and coorelating it across the entire verse is impossible.
The Course Books uses four seperate systems to break up its timeline:
Events within the Mage Wars and Age of Darkness use the B.G.A. System, dates during the Ages of the Alliance use A.Y., and dates after the fall of the Alliance use A.D. Each system has it's own zero and counting method.