Nan,
Time management is a difficult thing during the PMP because it is indeed a grueling exam. When I studied for and sat for my exam, I kept in mind that I had a maximum of approximately one minute per question if I was to finish right on time with no review. My goal was to answer each question in 30 seconds or less, thus giving me back valuable time for that review at the end. However, this method might make you focus on the clock too much, which isn’t ideal either. I simply looked at the minutes on the clock which gave me a rough estimate of the earliest question I should be answering and still meeting the time limit, a worst case scenario if you will.
My other technique was to know very well which point in the exam would give me the hardest time. For me, it was questions 100-150. I knew this from all the full-length practice exams I’d taken. When I saw question 100 in the actual exam, I had to steel myself a bit and re-cage my focus, because I knew that I was already tired and still had many questions to answer.
Biggest recommendation I can give you is just take one question at a time. Don’t focus on the fact that this is question 2 out of 180, for example. Take the exam in bite-sized pieces and you’ll do fine. Best of luck to you!