James,
I took an "eye break" about every 20-30 questions (depending how they were going). By that I mean I would stand up, turn away from the screen and stretch a little and perhaps walk around the chair (not the room). This would take less than 2 minutes. I also took a 10 minute break for bathroom and some water about 2:15 into the test. I think I was about 130-150 questions in at that point. I took one final physical break after I finished all 200 questions and before i reviewed the ones I marked to come back to. That was about 3:15 into the exam. Again - bathroom, water. Then came back to the look at the ones I marked and pushed the magic button at 3:45 min. My result was 5xAT. Seemed to work for me.
Harry