You can't check in for the BA flight until 3 hours before, as there will not be anyone at the counter...and security will probably not let you in the door until the 3 hour mark before scheduled take-off.

Make sure you notify the hotel as to your arrival flight into DEL, and they should have a car waiting to take you to the hotel...and they should take you to the international terminal at T-3 hours...hopefully for free. Do not take a bus or a taxi. There should be someone from the JW with a JW sign at arrivals. Just go to him and introduce yourself.

Get to the hotel, take a nice shower, a little nap, a little bite to eat, a little sip of beverage...then a nice civilized air conditioned car ride to the International terminal.