Our TA tried to get the air deviation when we first booked, but was unable to. He e-mailed back to me that you usually have to wait until 270 days before. Our cruise is next August, and when I reminded him to try again, he did. We are now down for the deviation and a $25 credit each.
I repeat, he said 270 days. We are more than 180 days out, but NCL now has us with a flight deviation. If it makes a difference, we are flying to Heathrow from Newark.