Mumbai
Start with the terminal, because at BOM it is not a detail you can fix at the last minute. Chhatrapati Shivaji Maharaj International runs two separate buildings — Terminal 1 at Santacruz and Terminal 2 at Sahar — and they are far enough apart that arriving at the wrong one costs you a shuttle ride and, on a tight turnaround, the flight itself. Terminal assignment on this route varies by airline and by flight, so read the boarding pass rather than assuming. The other Mumbai-specific hazard is the ground leg: departures cluster into a morning and an evening band, and the evening band collides with the city's worst road traffic, so for a 19:00 departure the honest question is not whether the seat exists but whether you can reach the terminal in time to use it.