I took a similar test but in person at an office a few years ago. Exact same layout, of "click when x appears, do nothing if not". It was only 25 minutes I believe but felt like an eternity. I had a 100% success rate and above average reaction speed, but I still "failed" because of my observed behavior as I was taking the test.
The proctor noted my restless legs, frequent posture shifts, and "tendancy to tap the table when not responding to the stimuli" (this was a strategy I had come up with to create something to do in response to "doing nothing", as it made a sort of rhythm that gave me something to do). I then realized that the test meant very little, but the proctor was watching and diagnosing me durng the test.
The proctor noted my restless legs, frequent posture shifts, and "tendancy to tap the table when not responding to the stimuli" (this was a strategy I had come up with to create something to do in response to "doing nothing", as it made a sort of rhythm that gave me something to do). I then realized that the test meant very little, but the proctor was watching and diagnosing me durng the test.