Simon,
With respect to preparing, I spent 10-12 weeks of dedicated study in preparing for the exam. I went from nearly zero understanding of PMI's way of doing business to doing quite well on the exam on the first try. Your mileage will vary, I suspect. With respect to "mad rush" the exam is given electronically and getting a seat is dependent on the availability of the third party exam provider (Pearson VUE), who is in the business of giving exams so you may or may not find scheduling conflicts with them. I'm not convinced there will be a "mad rush" with respect to Pearson VUE as their only job is to give exams. Personally, I approached it as it was a "personal project." I set the exam date 12 weeks or so in advance and then executed my study plan for it.
The time of the exam is completely a personal choice. At both 9AM and 10:30AM, you will be taking the exam over the standard US lunch time, so you will want to accommodate for that. Likewise, bring a snack anyway: Some nuts or a protein bar and water. You will not be allowed to take these in, but you will be able to take a break to get some water or a bite. I recommend a 7-10 minute bathroom-hydration break about 1.5-2 hours into the exam so that you can re-focus your eyes and clear your head to hit it again. That's just me though.
Good luck.
Harry
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Harry J. Elston, Ph.D., CIH, PMP