I do not have advice on how to manage your time so you can be prolifically productive, but I do think you've touched upon motivation being one of the main factors for deciding to continue on projects after work, projects that may even become your work. But discipline is the hardest yet simplest piece: you may not always be motivated, by discipline / consistency ensures exposure, ensures you apply yourself to your project(s) very frequently.

I suggest you read Coders at Work if you haven't already. It is a good compilation of interviews with living legends of computer science and famous software projects, and the interviews give insight into how each approaches his/her life. You might find some of it inspirational and insightful.

http://www.codersatwork.com/