You are excited about building things. At any point in time, you surely have a number of side projects on the go. So, what happens when that one extra project idea arises, and it's definitely one of those "hell yeah" opportunities? You don't necessarily want to drop anything, but you don't know when you'll fit in the extra time to take it on.
I share your predicament, and at Trampoline Day this weekend in Melbourne, I shared a solution that has been working well for me: I started waking up early. I have been waking up at 5am and putting in two hours of work on my new project before I head into the lab every day. This is in direct opposition to my natural tendencies: I've never considered myself a "morning person," and have always been inclined to work later into the night if I'm excited about a particular project.
However, I've found this new approach to be very effective. The early mornings are a good time. It is quiet. The day has just begun and my mind is clear of any distractions, so it is easy to concentrate. Because the time for work has a definite ending, it also encourages me to pick discrete and achievable goals for each morning. Rinse and repeat, and before long, I have demonstrable, consistent, incremental progress towards my goal.
Then, at the end of the day, I feel much less compulsion to try and fit in more work. I can instead spend that time enjoying the company of friends and family or doing other kinds of leisure activities (that is, before an early night's sleep early, since it's early to rise again the next day!).
This feels like a perfectly sustainable approach for creating an extra day's work of time each week for bootstrapping something new. If you have a project you want to start, or a new skill you want to learn, I'd encourage you to give it a try.