The time difference between New York and London is +5 hours. If it is 5 p.m. in New York City, then it would be 10 p.m. in London.
The flight time between New York and London is 7.5 hours, and the return trip takes 8.5 hours. If a person flew out of New York at midnight, he or she would arrive in London at 7:30 a.m. New York time. However, the arrival time when the touched down in London would be 12:30 p.m. These types of time differences are what causes passengers to experience jet lag when flying great distances.