The event did not even originally have experience bonus so it definitely was not the whole idea for them. What I said they planned the event to be a surprise and probably selected the final features and duration partly on based on that fact. I also did not say they hoped that people can not participate but that they knew that not all players would not be fully prepared so it would even it out the decisions or create balance.
Yes, even a week or month before is fine if they wouldn't take anything out.