My impostor syndrome briefly reappears every time I read articles like this :) I don't feel any state of "flow" or "zone" or whatever, and certainly wouldn't consider my entire afternoon ruined because of a single meeting in the middle as illustrated in the article. If there's a hard problem to solve, sure, I'll work on it until 4 AM because I have a hard time letting go of unfinished things, but that's mostly throwing hours at the problem and I don't think I'm massively more productive than during the day at the office.