The other thing I'd add is that, if you're working for yourself (rather than on the clock for an employer) there's no "rule" that you need to work 8 hours a day, 5 days a week, from 9 to 5!
Everyone is different. If you find you're at your most productive by working a concentrated dawn-to-dusk 12 hour day a couple of times a week, then why not bow to that discovery, and treat the rest of the week as days off. Equally, you could find that a couple of hours of work a day in the morning and again at night, 7 days a week, lets you get more done...
You may even find that it doesn't take very long at all to achieve what you want to do, so long as you hit the times when you're able to put in 100% maximum concentration and effort. Basically, experiment to find your personal "sweet spots" then work to whatever pattern fits you best, for exactly as long as necessary and no longer.
The biggest problem that you'll have to work to overcome is the nagging feeling of "guilt" that you're not getting "a full day's work done" which is reinforced by society at large. Once you're over that hump, you can enjoy your week and slot in your work as needed rather than feel you have to sit at your PC all day "filling the hours" just because that's what folks out in the real world do!