Recently went through this. Got an email at 2pm saying "please run through this exercise". Looked at the doc, then decided to hit it. I submitted everything back before 6pm. It was around 2.5 hours, and I took a short break in the middle. I screen-captured my whole session (not sent in) but to have a little souvenir of the exercise. There's really not much way I could have 'cheated' on the time because there was only 4 hrs tops between sending the email and submitted my results.
Their estimate was 'we expect this to take 2-3 hours', and they weren't all that wrong. I could see someone less experienced taking more than 2 hours just on one of the bad queries - unless you've seen the pattern(s) before it's hard to recognize and refactor quickly.