How long does it take to repair a leaking heater core? on 2001 Pontiac Grand Am

I have a family friend who is a mechanic who is repairing this for me. I am paying him. The leak was NOT coming inside of the car on the carpet and it was NOT fogging up the windshield, the heat still came out so I don't know where the antifreeze was going. I researched online and guys were saying a three hour job. But a guy I know said it would take eight hours. How long does it usually take? So I can pay him properly for his work?

Asked by for the 2001 Pontiac Grand Am
Heater core is 6 hours to change in this car.
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