I will suggest you to go to Ormara beach, it is around 6 hours drive from Karachi, around 2 hour from Kund Malir. It has very nice resort for overnight stay, a restaurant and very beautuful beach. I drove with my family and really enjoyed too much. You can leave in the morning from karachi, reach there around 4:00 PM, witness a beautiful sunset, stay overnight, have BarBQ and drive back next morning to Karachi.