So let me add my 2 cents having just about completed a International -> Domestic transfer in T3 @ DEL.

In short, plan for lots of extra time with your connection if you are transferring between a non-AI international flight to any domestic flight.

For AI international flights that connect to a AI domestic flight serviced by an "international" gate (i.e. AI 126 to HYD), unless your flight to DEL was on AI, you must clear immigration, pick up your checked bags (if applicable) and check in again. If your flight to DEL was on AI, then you can clear immigration at your final destination (as long as your AI domestic flight departed from an "international" gate) and save a lot of time.

All in, plan for at least 90-120 minutes minimum assuming you have *G status so you can skip ahead to shorter queues at check-in and security (and know exactly where to go to navigate the Byzantine process).

Oh and don't get your hopes up either on the AI lounge: as I sit here, it's 80 degrees with lukewarm beer with the pleasant soundtrack of table saws in the background, and no available showers. On the positive side, the pigeon flying around adds a touch of natural beauty to the experience.