The mods have all been asked to clarify the start of the Christmas Preparations Event for their forums, but as you already know it will be Midnight CET on Saturday (10th/11th) I am not sure how much clearer we can make that in our case, but here it goes:
For NL & parts of SKN it will be midnight, for LT & the rest of SKN it will be 1am Sunday, whereas for EN it will be 11pm Saturday. US will still be enjoying Saturday afternoon or cooking their dinner, but AU will be getting ready for lunch on Sunday & IN will still be asleep (could someone remember to poke them please). Finally, for WWW it will be sometime between 2pm Saturday and 1pm Sunday.
This is the Wascally one, making things much clearer for you