Hey, my experience about why it takes longer time to finish, mostly is because we spend too much time on some doubtful answers.
When i started the mockup exams, i used to linger on one question with 2 answers seeming to be both correct; which in return really consumed unnecessary time. So i adjusted my strategy where if i was not sure about which one to choose, I chose one i felt a better answer and moved on to next question while marking the question for later to read again.
By that, i usually finished most exams 20 mins ahead and used the 20 mins to go back to those uncertain questions and to give it a second thought.
The truth is, when you are unsure which one to choose, it does not matter you spend 1 min or 5 mins to debate, but rather a matter of 50% chance of guessing it right.
You know what, i actually finished the actual PMP test 40 mins earlier and i did not even go back to double check since i believed my first judgement and, i got 5 AT.