I doubt they were doing deep work in 3 minute chunks in line at the parking ticket office. One thing I realized for me is that simply priming the pump for later had non-zero benefits. Eg, doing a Google search for something, and just reading the result snippets counts for something in those 3 minutes. Reading the Wikipedia page on something isn't full actual proper research, but reading it five times (because you keep getting interrupted in the post office), but still managing to read it, counts as progress for later. Your brain simply just needs time to stew on things, hence the solution striking during a morning shower.

And much of a project, like life, isn’t deep work. It’s the thousand little things, things which are indeed doable in the interstices