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the time that he has done most of his posts was between 15:00 to 23:00 GMT time. He has near zero posts in the morning job europe zone time from 7 to 12.
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I would somewhat doubt that he only worked 5 hours per day. For someone as smart as him this is a very small amount of time to be working every day considering the standard work week is generally at least 35 hours (or 7 hours plus lunch per day)