Comment by kelnos
That's a perfectly valid comparison. A year's worth of hours is still a year's worth of hours, regardless of what time span I spread it over.
We use this sort of formulation everywhere. If I say I work 40 hours a week, no one is going to assume that I start work at 9am on Monday, work non-stop until 1am Wednesday, and then take the rest of the week off. If I say that people spend approximately a third of their lives sleeping, no one thinks I mean that they sleep continuously from birth until they're 30 years old, and then spend the next 60 years awake.
The point is that it's 8500 hours of free time used for exercise. It's time when you're not eating sleeping or working.
So it's not exactly the same. For people who have very little free time due to commute, work, children, etc. It's harder to spend half an hour of free time a day on exerciaing.
I mean I do agree with the premise that exercising is a good return (especially since the better sleep quality should be factored in) but I think the person you're replying to has a point when he says that saying it's one year of life is not really comparable