Chaotic raid bonus time- How does the timer works?

[Wawaya]

I think I saw it mentioned that it lasts for bursts of 3 hours up to 12 hours, on random data centers, and the bonus isn't even guaranteed but rather a chance at the bonus. So you could go through all the trouble of caring about the bonus, just to get nothing anyways...

Oh I am aware of the wonky distribution of Demimateria unfortunately, I wish they could change that for the next Chaotic, it was more about the timer, when does it appears, what triggers it, if it's not at the same time everytime, then surely it must be a rotation? But how can we know when the next windows will be up? Because seeing it at a certain time for multiple day in a row, then at a different time the next day, it's pretty confusing
I only care about it because it increases chance of Dais/minion/haircut drop