I was staying at the Grand Hyatt near the airport, and they advised if flying in J class, that I could leave the hotel 90 minutes before the scheduled departure, since there wouldn't be much traffic at the time the CX flight leaves (ie 3.50am)
I've always hated those middle of the night departures. But then, I heard someone say a new airport is being built somewhere in Mumbai (in navi mumbai? not sure of the spelling). If and when that comes up maybe they can turn to more civilized departure/arrival hours.