It will take around an hour to get through the airport but you need to decide what to do with your carry on bags. Do you plan to go to your hotel first to freshen up ? Where are you staying ? The airport is around 20 mins from downtown by taxi, or a little longer by metro.
At.mosphere ? Will you be dressed for a fine dining restaurant ? Look at the menus on zomato and see how much the prices scare you
There's not much to do after midnight other than bars and clubs. You could take a taxi and go for a photo tour before bed.
When are you coming ? The weather is warming up now and it's Ramadan in 6 weeks.
Your bags will be checked through for a transit of <24 hrs.