Ashfaq's junior mechanic Kashif changed mine in just 10-15 minutes.
BTW, my car was overheating and coolant was reducing about 1 liter a day. Therefore, the thermostat valve has now been removed that I had installed brand new last month (bought from Haji Autos, Plaza) and made the fan direct. This way, the engine performance and fuel average have been affected but eventually my car can stay on the roads as much I desire, rather than visiting mechanics again and again.