Hum, you said you did the job in 4 hours, lets see:
-there's always at least one or two parts or tools you need to run to the store to get. That takes at least one hour.
-tool clean up and garage clean up take at least 1/2 hour (probably more)
-putting your old coolant in containers and driving it to the shop for recycling takes at least 45 minutes
-cleaning the engine and parts of dirt and grease while everything is apart takes at least 1/2 hour
-test driving the car to let the air work out of the coolant system, refilling, and checking for leaks takes at least 1/2 hour
Thats 3 hours and 15 minutes already and you haven't even picked up a wrench yet. Did I get the old pump out in 2 hours and the new one installed in 2 hours? Yes. Did the job only take me 4 hours? Obviously not.
'84 300D, 175k
'90 300CE, 165k