that is one of the arguments in favor of the pomodoro productivity technique. For the unaware, pomodoro says to set a timer and do 25min of non-distracted work. Come up for air (mandatory stop) for 5 minutes. Rinse and repeat a few times. Some studies claim it takes 20min to get into the zone, but pomodoro insists on breaking that flow about 5 minutes later. The end result is training yourself to pick back up where you were at. I don't do pomodoro any longer but it was reasonably effective back when I tried it years ago.