The battle among Primordial entities could not be measured using normal time as a reference. Time and space were easily shattered and broken, leaving countless shards of chaos and corruption roaming about this space.
This meant that the flow of time could not be depended upon because it could stay still for an eternity or accelerate for trillions of years in a single burst. Everything was under the control of these entities, and all manner of changes were useless.
The elements of time and space were woven into their attacks, and so in Reality, outside this space made by Bahamut, the stable time that passed—maintained by the body of Primordial Time that had been shattered in a distant era—had barely been three days, but inside the space of battle, ten million years had gone by.
In the period where Rowan had been observing them, Bahamut and Chaos had fought for this length of time, and only now were they beginning to go all out.