What flights from Delhi take over 24 hours?
It always takes about 24 hours to fly that far. Such never related to aircraft speed but rather waiting in airports for connections.
I see that someone has already answered you, but I can tell you a story. I used to work at Intel, and one of my coworkers was an Indian woman (citizen nonetheless!), who was going home to the Bengal region to visit family. I asked how long her flight was, and it was something like 22 hours. I commented on the brutality of that, and she added that “The flight is less than half the travel time. Once I arrive at the airport, I have to take a series of trains and buses to get home, and that’ll take over 24 additional hours”.
So it’s NOT just the flights, it’s all the ancillary stuff associated with the flights that makes it difficult.