Delhi
Delhi anchors national governance, corporate headquarters, universities, hospitals, and a huge startup ecosystem, so departures from Indira Gandhi International Airport (DEL) remain heavy all day. Travellers on this corridor include executives, consultants, students, families, and medical passengers who often need immediate movement with minimal planning time. Mumbai is the single heaviest thing Delhi flies to, and the winter fog window in North India is the one predictable disruption worth planning around: December and January mornings out of DEL can slip by an hour or more, so an early departure with a hard meeting at the other end deserves a buffer. Because there are dozens of DEL–BOM flights a day, the practical move when a departure goes wrong is to rebook forward on the same corridor rather than wait for one carrier to sort it out.