Update 2 (Fri - 9:37 pm)
Guild is now over on Arthas. Happy inviting!
Update 1 (Fri - 1:31 pm)
I began the transfer late Thursday night. It is still "processing." I'm not sure how much longer it will take. If it doesn't complete by this evening, I will contact blizzard support to check on the status.
I'll keep you all posted here.