I'm not successful much at those, but when I am it is because I have circled the difficult parts. I think it helps me remember where the parts are in relation to my pencil marks, so I can find or remember parts of the passage when going back.
I would say that depends on the proctor... Ours was insanely fast... Best tip I can suggest is when they say pencils down, pencil down and right then move your watch.
Why do you think phones, mechanical pencils, digital watches, etc. are not allowed? Because LSAC is afraid of miniature cameras for recording test questions or answers. I would be astounded if they administered the same test days later.
I recommend doing a lot of practice with the "tri" pencil if you are going to use it. Great for bubbling, but I did not like it at all for extended use on the essay.