There's 2 places I've seen it first hand, restaurants and auto shops. When you have a mechanic/chef that can consistently pump out the work of like six people, and nothing seems to faze them, almost like they're anticipating every mistake and misfortune. There's a way of sort of lengthening the duration in a flow state, but the stress and pressure have to be something that actually pushes you. The people I've seen, know the basic tasks/jobs like muscle memory. They know exactly how many steps, and and what's the shortest amount of time each step needs to take. So then they can throw in multiple repairs/dishes into one seamless flow where they're constantly in motion, where they're uninterruptedly cranking out of finished products on top of the required prep work. Of course, this is a lot easier in both those situations when you're working as part of a team.

There's a difference, imho, between doing it with routine tasks you've already mastered, and learning something novel. An issue I'm seeing with a lot of Gen Y-er's is the lack of appreciation for silence and purposeful contemplation that's required to actually get a handle on a learning curve. Your point is valid, there's no use in a flow state if you don't have the capacity to maintain and utilize it.