One of the most-asked questions that I see on social media is how long it should take to study for a certification exam. The answer isn't as straightforward as you might expect.
In truth, nobody can know how long it should take YOU to prepare for a certification exam. Everyone is different. Some people learn quickly, and some people learn slowly. Some people require a lot of hands-on experience, and some people can pick it up just by reading a book. Some people have never seen a router, and some people have administered networks for decades. Some people have many responsibilities (school, spouse, kids, job), and some people have no responsibilities at all. Some people can stay focused on studying for hours on end, and some people need to study in small chunks.
So it could take you less than 10 minutes to study for an exam ... and it could take you more than a year. I'm guessing you'll be somewhere in the middle.
Setting yourself an artificial deadline can cause you to over-prepare or under-prepare. For example, if someone says that you should be done in three months, you might pressure yourself to be done by then, causing you to try before you're truly ready. On the other hand, if you feel like you're ready after one month, you might wonder what details you're missing, causing you to delay unnecessarily.
So how do you know when you're ready? That's what practice exams are for, such as Boson's ExSim-Max practice exams. You should take each structured practice exam as if it were the real thing. After taking a practice exam, study ALL the explanations, even for the questions you answered correctly. Know why the right answer is right and why the wrong answers are wrong. If you've got any weak areas, use your study guides and the linked references to shore up your knowledge.
Keep in mind that a practice exam can accurately gauge your ability ONLY the first time you see a batch of questions. After you've seen a batch of questions once, you will begin to memorize the answers, which can artificially inflate your test score the second time you take a practice exam. So don't just take the exams over and over until you get 100%. The most important thing is to understand the concepts, not to memorize the questions.
By the time you reach the last structured practice exam, you should be doing much better than you did on your first structured practice exam, especially if you've studied those explanations along the way. Your progress should give you confidence that you can tackle the real thing.
So how long should it take you? As long as it takes. You've got this!