Hello Sheilla,
The most suitable time to take your break during the exam is mostly about your time management.
In my opinion, the best time is at midway during your exam, around the end of the second hour.
But you should be monitoring the pace at which you are answering questions. The average of 60 seconds per question could be a good one, and practically, it is good to see where you are before deciding to go for a break.
Taking a break is optional. You said that with the PrepCast Exams you were not taking a break and still making good scores, that will be up to you to evaluate the real situation you will face during the exam if you will have the same level of confidence, that will be good. But remember, it is your time management. If you feel comfortable with the remaining numbers of questions comparatively to the rest of the time, the ability to take a break is an advantage you may think to exploit because that will help you to perform even better for the rest of the exam.
Those are my points, and I hope you may find them helpful.