It lasts as long as it lasts. I'm in the 200lb club, I ride a heavy bike, and I do a lot of hills-- so I'm lucky to squeeze 1200 miles out of a chain. But the chain is the cheapest part of the drivetrain (usually) so better to replace it early than find yourself replacing the chain, the cassette, and the rings. It's not a hours/days/weeks thing. When it's worn, it's worn. No two riders or situations are going to be alike.