I made it from gate to gate (Air India International -> Air India Domestic) in about 60 minutes. I was helped by my business class boarding pass. I landed from IAD at around 10:15am, and was seated in the front exit row so I was off the plane right after business class passengers. I hustled to immigration and went through the business class line, which was short (2 passengers in front of me). I waited a bit for luggage but once I got my luggage I went out the green line and turned left like the instructions above say. The nice security man looked at my boarding pass and said "hurry!". I went up two levels to departures via the escalator, and found the business class check-in counter at Air India. They took my bags, then I went through the business class security line and hustled to my gate.

If you are spending a few hours in the domestic terminal, it's nice enough and there is a Centurion Lounge there.