if that's a domestic flight and you have more than 24 hours, I'd say go to the aerocity and book a hotel there. Much less expensive, you can walk around, have a good meal or two, and easily come back to catch your Kolkata flight.

There is a Holiday Inn in both the domestic and international terminals. I would email the hotel and they will tell you which hotel to make a reservation depending on your flight.

Yes. I believe that is correct as long as your Int’l flight is also leaving from T3 the next day. If departure is in another terminal, there is an offsite hotel connected by tram you can stay in.

Hi, yes this is a 24 hour hotel, and the airport seems as busy then as anytime! Just book a one night stay (dated the day before) and note that you’ll be a 3:00 am arrival following morning. You will need to clear C & I, and then go through the process of phoning the hotel desk from the arrivals hall. It’s a bit lengthy but straightforward. Expect to be in your room by 4:00 am. On departure, you’ll be taken back down to the arrivals hall. Have a great trip!