True, it was already source-available. That was already quite nice, especially because it meant I could fulfill my completionist urge by reading the source code to see everything that could've happened.
The change here is that it's been GPL'd, so you could (legally) build another game using parts of it if you wanted.
I'm not sure if this is cheating, but I set auto-clicking on the buttons with the console and left it open in its own tab so that I could do other things while my minions created steel. Certainly my time spent was considerably less than 4 hours.