Starting your own business has many different sides to it. You need to learn to become business orientated as well as understand things like accounting, marketing and networking. Many people legitimately have a great idea, dev it and then fail as they have zero skills in marketing and business. If no one knows your product exists, how can they use it. Also, market research. Don't assume someone wants your product if you haven't asked (this doesn't include your friends and family).
On top of that enjoy the grind; you hours will be 24/7 at that point. I used to run a part time web business while I was still in SA. To make money you have to offer one (or more) of the following: better service, cheaper service, better product, cheaper product.
I made money because I was willing to entertain phone calls from my nutjob clients at almost anytime (sometimes 24:00 - 02:00 in the morning) coupled with decent services at a lower than premium rate. You slowly build up to a point where you no longer have to deal with that type of thing as you have easier clients to deal with that can replace these, but in the beginning it is definitely harder.
In a way, the 8-5 is the easiest thing you can do. It does however waste massive time and resources and any business that is getting more than 3-4 hours of proper output from an employee during a 8-5 is winning in my opinion. If people were left to their own devices the would probably be happy to work on that bright idea they thought about at 9:30pm, but because they were forced to sit at a desk from 8 - 5 they will put the idea off (and lose the enthusiasm) until tomorrow. Even in the software dev arena, I've read sooooooo many articles about how companies are embracing flexi time and remote working, yet only few put it into practice and put very stringent controls on it that it is not even worth mentioning in the first place.