It takes approximately 10 to 15 minutes of focused attention to reach a flow state. Once in flow, it may last from 30 minutes to a couple of hours. However, it is possible to achieve flow more than once a day, given the right conditions
time to enter flow state
HEARTBREAKING: Software engineer has to turn around, take out one earbud, and say "huh?" when someone asks them a question even though they finally got in the coding groove (View Tweet)
For an individual focused on deep work, it’s easy to identify the relevant lead measure: time spent in a state of deep work dedicated toward your wildly important goal. (Location 1526)
Also consider the frustratingly common practice of forwarding an e-mail to one or more colleagues, labeled with a short open-ended interrogative, such as: “Thoughts?” These e-mails take the sender only a handful of seconds to write but can command many minutes (if not hours, in some cases) of time and attention from their recipients to work toward a coherent response. (Location 671)
For an individual focused on deep work, the implication is that you should identify a small number of ambitious outcomes to pursue with your deep work hours. (Location 1509)