I did the UMAT in 2017 and got 97th (192, 61/70/61) on my first try (how I did, I have no clue!). I also did it from front to back because during practise exams I did, I generally found that I had less time if I did it section by section that if I just went through it chronologically. Another thing is that if I got frustrated with a question, sometimes it could lead me to feel frustrated about other similar questions in a section which was bad - so doing a question from another section meant my brain could reset itself, etc. I did the same as another poster as well in that I circled questions which I thought were taking me too long, skipped them, and went back and did them at the end. I finished with about 10 minutes to go and didn't miss any questions overall.