between 6am and 10pm it is 16 hours.
say lhr-jfk takes 6hr and 1-2 hr on the ground turnaround
2*6+1.5*3=17 hour they could just make it! (but right)...i vaguely remembering seeing some asian magazine on the lhr-jfk flight (but extremely vaguely, anyone else picked up clues like this?)