I mean, from what I understand, the krillrolls move around like that to give everyone the option of playing. (Assuming certain times are bad, one should eventually be good for your schedule.)
They are held every X hours, that's why they keep switching around. The 1.25k Krill freeroll is every 100 hours, which is not an "even" number when it comes to 24 hour days. I like it the idea in that it gives people every opportunity to play in different time zones around the world.