Chaotic raid bonus time- How does the timer works?

[Wawaya]

Very straightforward question but: How does it work? Specifically- How does it activates?
Is there a weekly rotation? I've seen it activates at two different time since release. Does anyone have enough information about this? What did you saw on your own servers/datacenters?
It's pretty annoying to see the bonus being up at a certain time, let's say, 12PMST for 6 days in a row, then the next day, it's at a different time, on the same server, especially when it'll last for an undetermined amount of time. If there is a way to know when the timer will rotate, and if somebody figured it out, please share it (It's not about Demimateria distrubtion, only about the timer window)