Can't allocate enough time for my idea!

I'm working a full-time job at a startup, and I have no reason to quit or change the job. It's a good culture, I'm learning new things, I have high autonomy and working on things I enjoy ...

But I want to start my own business !

I have an idea that's been in my mind for more than a year (that's a record). And it scores 10/10 off the shelf in many regards (bootstrappable, existing market, a clear way to acquire first customers ...)

But I find it hard to allocate time to work on it on the side (I made some progress but it's not enough)... and I can't quit my job because I need the money :/

What are your thoughts?