The ticket says the flight leaves London Heathrow at 11:25 and reaches New York JFK at 14:20 on Monday 14 June 2027. On the clock that’s 2 h 55 min, but the two times are in different zones. 11:25 in London (UTC+1) is 10:25 UTC, and 14:20 in New York (UTC−4) is 18:20 UTC. The flight takes 7 h 55 min, and New York is five hours behind London.
The other way round, the printed times look longer than the flight. A 19:30 departure from New York that lands in London at 07:25 the next morning looks like 12 hours on the clock, but it’s 6 h 55 min of travel. The arrival-time calculator works that case out from the departure and the duration.