Final update:
Flight scheduled for: 00:10
Checked-out of hotel: 14:00 (hotel was only 5-10 minutes away from the airport; Aerocity JW Marriott), so I decided to take a taxi and drive around the city for a while.
Got dropped off at the airport: 18:00
Went to use the Allways waiting lounge/area: 18:00 - 20:00
Entered the check-in area around 20:05
Check-in counter opened around 20:30
Security/immigration took about 5-10 minutes in total; ended up spending the rest of time (20:45 - 23:15) at the lounge and then walked to the gate.
Next time, I'd much rather stick around at the hotel bar or restaurant instead of waiting at the AllWays waiting area/lounge.