I feel your pain. I'm also dayjobbing while working on creating a startup. The conclusion I've found is that working this way makes it much slower, but not impossible. The hard parts are a: not giving up (actually, that hasn't been hard), and b: using the time you have efficiently.

There are a number of paths available to you: 1. Give up. 2. Quit dayjobbing, go full-time on your savings in hopes it will succeed (part-time freelancing is a partial version of this). 3. Get funded and work off the funding. 4. Get a revenue-generating product out the door so it starts paying for you to work full-time.

I don't believe in #1. I can't do #2 because my marriage is more important than my startup. I looked into #3, but fundraising is a full-time job that takes your eye off the ball with no guarantee of success. This leaves #4.

So consider a way to build a subset of your product you can sell, or otherwise shorten your takeoff trajectory. That will get you going faster.

As for the freelancing idea... unless you think you can immediately get half-time freelance work and keep a steady flow of it, it's not a good path. It will start intruding on your startup time.