Ignoring the ethical complexities here, which are inherently subjective, and the legal issues, which I have no authority so speak on, let me just say this: writing code for your side project on your work computer is
really fucking stupid.
It's not a gray area; there is precedent and you will lose.
Once in my life (first job out of school) I was in a job where I'd been relegated to menial grunt work that wouldn't teach me anything or advance my career, so I've been in the career sand trap. What I did: I taught myself Python and a few APIs I needed for the side project (which was actually a research project, not a startup) during slow periods. I did a bit of research into AI algorithms (on Wikipedia) as well. But I never wrote code for the project at work.
If you must steal ("liberate") time, be very careful not to write any code that you'll need when at work. I'd say 3 rules apply.
1. Generally, a company can own what you do, not what you learn. If you're going to steal time, use it to do research and exploratory code (that is thrown away) but keep your product code 100% on your own resources. I'm not saying this strategy is right, nor that it's a fool-proof legal defense, but it beats the alternative (of writing side code at work) which is generally considered both wrong and illegal. As far as I know, there's no legal distinction between reading AI articles on work time and the million other kinds of goofing off that 90% of corporate denizens spend most of their days on.
2. Companies want you to work 9-5 because those are your best hours. If you're serious about a side project, then the first thing to do is to figure out if you're a morning or a night person (which is mostly genetic). If morning, start waking up at 4 and use 4-8 for the project. If night, your side project should be done in the evenings. You can only give the side 33% of your work time, but you can give it 80% of your energy by aligning your most energetic hours with your side project time. If you're not serious enough about a side project to make these adjustments, you're not cut out for it.
3. If you get a creative "spark" at work and must get an idea down, have a legal pad and pen that you own (i.e. not with the company's name on it). Write down your design and implement it later. Poets may lose it if they don't get it down at once, but you're a programmer, not a poet. So get your ideas and maybe some pseudocode on paper, but no code goes into any machine until you're home and it's your machine.