This is good advice, but even when things aren’t planned in this fashion, there is still a good chance you don’t need to work long hours. I only work more than 40 hours a week a couple of times a year, and even then I’ll generally be able to work fewer hours the following week.
The trick, in my experience, is to just make sure that you consistently sign in and out of work promptly (at 9 & 5 in my case), and that people know they can call you for a true emergency. Working someplace that’s not a startup also helps.
I think this is a great idea, I wondered how many people besides OP has put it into practice?
My workplace does but we develop software for internal staff. We almost never work over 40 hours. It’s great and we get to focus on whats most important and work down from there. Occasionally something that wasn’t important becomes important and we reorganize the list. There’s always like an infinite well of work (obviously) but we manage the incoming work pretty well and the “customers” are quite happy.