The amount of time that it takes people to prepare applications is very individual and varies widely - a lot depends on how clear you are on your career plans and overall story, how much school research you've already done and what your writing style is - ie, some people can crank out well-written essays without a lot of effort while others need to go through numerous iterations.
Different people also use the Lab in different ways -- that is, some of them go from start to finish on all aspects of it, whereas other simply sign up to read the essay guidance. There is also "homework" in the Lab such as reaching out to current students, which some people have already done but others haven't.
Finally, some schools have pretty simple essays whereas others, like Harvard and Stanford, have much "tougher" ones and thus have much more advice on how to tackle them. As an example, our advice on the HBS essay and application contains about 3 hours worth of videos and examples alone.
Long story short, we can't answer that question for you - only you can!
You'll find though that ApplicantLab helps you break down the application process into all of the different elements, and the great thing about it is that you can go through all of the advice and guidance on your own schedule and whenever works for you!