Just add some comments.
I think Linux Academy did a better job in the professional course than other courses since you have a wider and useful coverage.
I have a full time DevOps job and I spent all my nights and weekends on AWS study since May 15th, 2016. I got all 3 associate certificates quite easily by following other courses alone. But it took me almost two months for this one. I didn't watch re:Invent videos since they are too long. I read white papers and user guides for deeper knowledge.
Even I didn't sleep well, I was very confident that I could complete the exam in time so I didn't rush to finish it so I read questions from beginning with my normal reading pace. And even English is not my first language, I didn't find it a problem for me to do the exam. I have about 25 minutes left in the end and reviewed marked questions.
I did a lot of memorizing in the last week before the exam, just like what I did in the university exams.