I can't squeeze more than 4-6 hours of intellectually productive hours out of a day. I may delude myself into thinking I can do more, but it's not sustainable.
I used to have really bad habits with respect to keeping my apartment clean. Not dirty, but just generally messy (bathrooms were terrible though, I'll admit). And it was because of the time it would take to do it. Acknowledging my true time budget I now keep a nice, though not spotless, apartment because I take 15 minutes each day to straighten something up. Some areas need a Saturday morning to tackle. But the bathroom is cleaned once a week. The floors get cleaned throughout the month in segments.
If you've ever spent time on money management with tools like YNAB or Mint, it's very similar. You realize where your time is going, and what time is left available. You mete it out in reasonable amounts to the tasks that need to be done. When I'd only clean my apartment once a month (at best) it was a major undertaking. It was intimidating and I'd skip months because of that. Amortize the time cost across the month, it's now "easy", and my apartment takes 20 minutes to get ready for company in the worst case of short notice from friends.
I see statements like this on HN a lot, particularly from developers (myself included), but most of them cringe at the thought of having 2-4 hours of administrative work every day.
This correlates with my anecdotal observation that the smartest people can write bad code, and it takes them quite a while to absorb the stuff of writing good code.. a couple years at minumum perhaps. Its not just about raw thinking power - perhaps the important bits are, but not all of it.
I do this all the time. Of course, the person new to it is usually myself.