June/July is still a good point to start the offer. 18th might be a little arbitrary, but it's no more or less probable than any other date really. Bearing in mind most people with a BAPP would tend to use Amex for booking holidays anyway because they've shown themselves to be Avios hunters and need the spend for the 241.

There seems to be a general impression that Amex are going to be nice and allow spend for 241 and nTPs and so on to run concurrently. Amex is a rapaciously efficient business, and it will know when spending tends to land. Summer holidays are paid for by May mostly. The offer is to drive incremental spend, not reward what will happen anyway.