That is tough, been trying the part time route for almost a year. Realized, if nothing else, the delays in implementing would obsolete the idea.
A year ago when I started, there were just 2 major competitors to mine, after a year of working on it part time, now there are half a dozen more good competitors. Not trying to be a skeptic, and I also had other factors against me.
Finally I have decided to quit my job soon and focus on the start up full time, Otherwise I am sure the one I am working on now won't even have a sliver of a chance at success.