I don't know, a trip to the USA is a bit of a big undertaking for a last minute trip. People will make quick trips to the continent at the last minute but I personally don't see a majority if pax being last minute bookers.
I've no idea of the pax profile and the breakdown of those on business or on leisure so I can't be certain and there will always be those who book last minute based on need or work, but I can't see these being in any significant numbers.