They say you should work smarter, not harder
What you ask is possible but it is rarely achieved and never before putting everything into the frying pan. That means that at least the first year or two you'll be working as hard as you work in your current job, if not more because you have more to gain by being your own employee.
Definately, even if you were dedicating full time to this project, you should outsource the bits and pieces that you can't do on your own (either because you don't have the time to learn the complexities yourself or because your time will be better spent somewhere else)
You can start easy and then build up from them. So, let's say, if you're plan is to monetize from a blog, use a WordPress blog and start writing today and setup a schedule of writing an article per two weeks. Fill it up with content bit by bit. Start to advertise using Google or any other company. Once the blog is giving some cash, then you can think how you want to go on.
To be a blogger, you don't have to leave your job. Now, if your well-studied and built business plan requires something else, you will have to decide if you believe in yourself and your plan to take the risk and dedicate your full attention to it