Went full time on our side project, https://emailoctopus.com, last year when we hit the $5k a month mark. We'd been working on it for 3 years and had some steady growth - contracted a few days a week alongside until I could afford to go full time.

In hindsight should have done it sooner, a year on we've grown so much more by taking it seriously as a business. We value our time more and as such charge more, yet growth has only accelerated.