I'm not the only dedicated professional who takes his work seriously enough to stop doing it around dinner time. Cal Newport is a computer science professor at Georgetown University. In addition to being a productive academic, he's also written several successful non-academic books. 
In Deep Work: Rules for Focused Success in a Distracted World, Newport introduces a concept that he calls fixed-schedule productivity — to optimize your productivity, begin with a commitment for how much work you'll do. Newport's commitment is the same as mine: I don't work after 5:30, and I don't work weekends. Newport's productivity is more intense than mine — during his first three years teaching at Georgetown, he's published twenty peer-reviewed articles, won two competitive grants, and published two nonacademic books — but what we would both agree on is that our productivity isn't despite the fixed-schedule commitments we keep, but because of them.
So why, exactly, does that work? Newport gives two reasons.
First, fixed-schedule productivity (FSP) forces prioritization. Newport categorizes work as deep or shallow; as a teacher, I might categorize it as stuff that's most likely to promote long-term flourishing and stuff that's not. For Newport, as a professor, he's careful to limit anything that takes time away from conducting original research — that's the deep work of his profession, and that's the work that's most determinative of his career trajectory and his contribution to his field. For me as a teacher, I've learned to largely leave my bulletin boards alone (I try, and often fail, to keep an updated word wall, but that's it — there are yellow posters on my board that used to be white), to do email one to two times per day, and to grade efficiently and purposefully. Doug Stark, author of the Mechanics Instruction that Sticks series of mechanics mini-lesson warm-ups, has some similar strategies.
Second, FPS forces conscientiousness. When taking the papers home to grade them isn't an option, I have to get grading done as quickly and purposefully as possible. I can't grade AoWs for four minutes apiece because I wouldn't possibly be able to then plan lessons or read like a professional. I'm not free to believe that I can afford to check my email nine times per day, or that it's possible for me to check the news every half hour (a ready temptation for me these days), because inevitably 5:30 comes and the work day is done.
In other words, starting with the constraints isn't just a Dave Stuart Jr. folksy-wisdom thing; it's a Cal Newport productivity guru deep thinker thing. Thanks, Cal. (And thank you to Mary Clark (@semslibrarylady) for sharing this great book with me!)
- I've not read all of his books, but I can vouch for How to Become a Straight-A Student: The Unconventional Strategies Real College Students Use to Score High While Studying Less (I've drawn from it for teaching my own students), How to Become a High School Superstar: A Revolutionary Plan to Get into College by Standing Out (Without Burning Out) (it advocates for a focused approach to high school versus a “do it all” approach), and Deep Work: Rules for Focused Success in a Distracted World (which I cite in this post).