You won't be allowed into the international terminal of BOM till like two hours before your flight, so perish the thought of hanging around in the lounge for several hours.

I would suggest that you leave your bags at your hotel, finish whatever you need to do in bombay, including sightseeing or whatever else - and then take your luggage over to a bar that's close to the airport, get some dinner and a few drinks before you head to the terminal.