From Labyrinthe Wiki
The Final Dawn is the term given to the auspicious event that marks end of a Primal year and the beginning of the next. As the last night ends the Final Dawn of that year then marks the beginning of the new year as the first rays of the new year fall upon Primus. In calendar terms the Final Dawn of say, IM 1008, would refer to the last day, or sometimes the last three days of the year IM 1008.
Over the Period of the Final Dawn the World Spirit of Primus walks his world and through the eyes of the City Spirits, filtered through the eyes of the Realm Spirits observes the world and at the passing of the Final Dawn that which is of significance becomes fixed in place in his mind and thus sets reality for the next year.
At the passing of the Final Dawn, unless extreme measures are taken all rituals end, their power fades and they must be renewed, however on the converse side many forms of rituals which cast throughout the year, which might last but a short time otherwise, if cast at just the right moment at the Final Dawn will be regarded by Primus as the natural order and thus are sustained for the entirety of the year. So, for these combined reasons the Final Dawn a very important time for ritualists and at any given Final Dawn most powerful ritualists will be ensconced in their Ritual Chambers or other places of power, for at this time, with their rites diminished or destroyed they are relatively vulnerable and they will often be found enacting new rites to assist and protect them for the coming year.
Those skilled in certain arts, and not always just ritualists, are able to draw the gaze of the Primal Spirit either bringing things to its attention or hiding things from its sight. In doing so things that might otherwise pass unnoticed by the Primal Spirit are recognised and given a significance that perhaps they are not due and things that should perhaps be seen are wrongly forgotten by the Spirit. This can have a profound effect on the reality of the next year if such meddling is left unchecked
Thus it is easy to see that the malleability of reality at this point in time means the Final Dawn is of supreme ritual importance in the Empire and across Primus in general for through ritualism or cunning the definition given to the world can be manipulated by both those seeking to better the world and the unscrupulous seeking to alter it for their own ends, perhaps even initiate something as serious as a Convergence. Consequently during the period of a Final Dawn, typically culminating in the last three days of the year, the Empire, usually led by the ever vigilant Imperial Inquisition, large numbers of Mercenaries are gathered to deal with hostile ritualists, other worldly forces or other emerging supernatural threats that take the opportunity to enter Primus and seek to impose their own reality on the world, a reality that might prove detrimental to the stability of the Empire and the nature.
The Final Dawn also is the time when entropy, the waste matter that is generated from the enacting of rites, that has accrued over the past year, is washed out of the Empire through the entropic sink of Port Miere, freeing the Empire of dangerous build up of this ritual waste.
Once every thousand years, a very special Final Dawn occurs, referred to as the High Final Dawn, this marks the end of an Age and the death of the Primal Spirit to be reborn.