It's usually best to call in sick with the possibility of you showing up late every patch day, I've had raid days on tuesday where I had no intention of raiding because of no HB turn around on me because HB was updated.
We can assume they have US accounts, but you also have to assume they want to research into all/any security measures blizzard might have added/changed. You can usually bet on the fact they had a working PTR build so it's just a matter of double checking everything which still takes time.