Damien was in a justifiably selfish mood.
He didn't know how long he could wait before his main body would be forced out of the Void, and to extend the time he could spend with his wives as much as possible, he intentionally distorted the Sanctuary's time flow to be far, far slower than reality.
Not like it meant anything. The lower universe was just an empty Abyss now, so there was no real-time flow to use as an anchor anyway.
His main body was also in a place where the concept of time didn't exist. While he'd spent over 5,000 years in Grand Heavens Boundary as Alexander, he couldn't say how long it had been since he entered the Void.
Because he truly didn't know.
It was a strange situation where he couldn't anchor himself to any flow of time no matter how hard he tried, so determining his stay in the Void in terms of time was just not something he could do.
In the first place, it wasn't applicable to him.