Hi, Pang, good day,
Let me answer your questions:
1. It is optional. You can click on the "finish" button if you want to finish the break period earlier than 10 minutes.
2. You have to submit the first part of the exam, containing 90 questions, to initiate the break session. Essential to informing you that you will be able to review it later on.
3. 10 minutes of break time is extra time, not included in the 4 hours duration for answering 200 questions in the PMP exam.
4. Screen time count down will be displayed on your screen and the "return to exam" button that you must click on to return.
5. Yes, I used this 10 minutes to relax a little, use the bathroom, and drink water. It's advantageous, and I recommend you to use it.
I hope that my answer clarifies your questions. If you have further questions, do not hesitate to write it down. I would be happy to assist you.
Regards