I wouldn't worry about getting that wrong, as its an operational decision that is likely based entirely upon the ride crew and how they're handling things. I'm sure the expectation was to have it running from the 20th, but if they need to give the crew additional time to get up to speed, they can do that pretty easily. I would also not be surprised to see them do "surprise" Express usage for brief periods the few days leading up to the 20th to really test the crew on that.
K&K is a different story, though (not sure they can complete it and get the necessary cycles by the 20th).