4 hours a day for 8 weeks?

That'll all depend on how much you know of your own studying methodology.
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Some people learn better when they listen to lectures, some people prefer books over anything, some people just do ungodly # of practice problems, and as long as they all do that effectively in accordance w/ their learning preference, they can all pass.
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W/ that said, I studied at least 3 hrs a day every weekday for about 3 months per section. I increased the hrs and studied over weekends as well 2 weeks prior to the exam. I took a week or two off after each exam.
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I've seen people pass all four sections in 4 months. 9 months. 1+ year(s). I also know someone personally who's been studying for ~4 years and still didn't pass all four. I think she passed a couple of the sections, but they all expired.