The test blurb estimates 20 minutes. How long it actually takes depends only on how long you spend making up your mind which face to click. I didn't take more than a few seconds on any of them, because if I don't recognise a face in that time, I don't recognise it and should just click my best guess and move on. I didn't time myself, but I believe I took rather less than 20 minutes. (89%, despite my subjective impression that faces with all the rest of the head cropped away look pretty much alike.)
My experience mirrors this. I felt like I was guessing hastily most of the time but in the end, by going with whichever face seemed more vaguely more familiar than the others, I ended up with an above-average score.
The next installment of the Polling Thread.
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