The world's longest nonstop flight now lasts 19 hours and 20 minutes. This record is based on block time, which measures the total time from when an aircraft leaves the gate until it arrives at its destination gate. Block time includes not only the time spent in the air but also factors such as winds, airspace restrictions, and taxiing.
There is recognition that any airline could potentially schedule a long block time and claim the title of the world's longest flight. However, using this metric, a new record has been set for the duration of a nonstop commercial flight.
Block time differs from actual flight time as it accounts for operational realities beyond just flying between two points.