Honestly I think the dirty secret is most peoples work output, especially in white collar work, is not linear. I'm willing to bet if you are even able to quantify your output (I don't believe most people can do that unless they are merely a fungible cog in some production process), you'd get the same exact amount of work done in a year working 4 10s or 4 8s or 4 5s I'd even bet.

Think of the classic case of the deadline and what it actually means. Case A, you didn't procrastinate. You took plenty of time to think on the problem, work on a solution at an unhurried pace, put it aside, come back to it, and solve it before it is due. And then, it is done.

Case B, you did procrastinate. You have no time at all to think all day, you immediately do and iterate. Four hours later you've sprinted and delivered. And then, it is done, same as it would have been if you didn't procrastinate, maybe 10 fold reduction in time.

And that is worst case examples. Typical case is probably somewhere between these A and B, but the point is non linear time to output.