I have explored Karachi but have not spent much time there. I have been to Askari, DHA, Beaches, I.I. Chundrigar, and some other popular areas. My cousins in Karachi are not in-door types.
The Middle Class in Lahore is heavily bogged down in "earning related efforts." This class gets time for outdoor activities mostly on weekends.
However, I notice lot of traffic in Lahore on almost daily basis. So it is likely that people somehow make time for outdoor activities. Traffic declines only at night time around 11 pm mark.