Start by writing a description of the project
Write 200 words. This description clarifies the project in your own mind. Once it's on paper (or on the computer screen), you'll have a much clearer idea of what you need to do, and when. You'll find that just knowing this goes a long way toward eliminating procrastination.
Most writers start as "weekend" writers, writing when they have a few moments of spare time.
You can transition to a full-time writing career, if you're organized. This article gives you a nudge in that direction.