You will not become an overnight success.
That's a down note to start out with, but it's also very true. You will not become an overnight success. The reason for this is because when you are first starting something, you haven't yet put in the hard miles in order to succeed. You haven't gone down the different avenues that can lead to frustration and despair that can bring you to a crossroads of either continuing on or giving up.
The creators you see who seemingly come out of nowhere have put in the hard work, and they've been able to position themselves to have their work seen by people who were able to give them a bigger break working on a company-owned character. Sure, some of these people were born in special situations that lead to them being able to really be seen by editors where most of us would have trouble getting in the door, but understand that editors aren't going to hand out jobs to just anyone, no matter who they are. There are publishing mandates that state the quality of the work has to be at a certain level, and everyone must at least work at that level. (It doesn't matter what your personal opinion of someone else's work is. If they're able to sell books with whatever their skill level is, then they'll get hired. This is the only explanation of Rob Liefeld.)
It will take however long it takes in order to become a success. It could be six months, it could be two decades—what matters is that you put in the hard work in order to become good at your job, so that when opportunity comes your way, you're ready to answer the call.
You will not become an overnight success, but that doesn't mean you can't prepare for it now.