Everybody tries to get to the best position possible in Arena by 6pm local time, right?
It's 6pm first in the East Coast, then Central, Mountain, Pacific (for the US).
So all the East Coasters play arena at 5pm local and push the rest down. An hour later, all the Central guys do the same, and push the rest down. By the time the West Coast guys open up arena at their 5pm, their rankings are demolished!
I bet all they guys complaining that they went from top 10 to past 100 in one day are west coasters...
Saves East Coasters a 50 crystal refresh for the second five matches, I guess...
We only got to deal with western europeans, but that gives us a solid 5 hour window of relative little arena activity.