I was a full time Manufacturing Engineer in an Aerospace Manufacturing company until I decided to dive into the A.I space and focus on Machine Learning. Fortunately around that time I implemented an ERP system at my company. I taught myself SQL, SSRS and some advanced customizations of the ERP system and began building Business Intelligence tools and reports. With remote friendly and company valued skills in hand, I asked to go part time remote so I can spend more hours programming and tackling ML projects.
One year into it now, I work 20 hours remotely for the Aerospace company, and spend about 20 hours to a ML project with another two researchers, then the rest is on personal projects / development work (website building, reading, non-ML projects).
My take on it is that the hours with my Aerospace company are easy to tackle. Specific objectives, set amount of time to complete, and your success as an employee is measured by deliverables. The other hours are loosely defined, open ended and possibly more mentally exhausting if you are trying to learn new skills.
I would recommend picking one tangible objective / project to spend your extra time working on, otherwise I think the hours will be under utilized.
My experience is that the first few months I spent learning a lot of different things in CS / ML. After a while it started to not feel very satisfying, because I wasn't gaining a mastery in any one thing and I didn't feel like I had much to show for it (aside from proclaiming 'I learned about a bunch of different things!').
With the internets infinite resources, it's easy to pass the days just wandering through the vast stores of knowledge out there (or get lost in hacker news or Wikipedia). If you don't have a fiery passion for something specific, it may be even harder to work effectively during these hours. The other option is to not work on anything and just do as you please, but I don't find that particularly satisfying myself. So my recommendation here is to go into part-time with the intention of building a very specific skillset / work on a specific project.
Once you have a very specific objective for your personal-work hours, the flexibility is glorious. I have the freedom to exercise, meditate, even power nap at whatever time I see fit. I can work through lunch or take a long one with someone, work from the library, co-working space, office or home if I please. These activities do take up time, but because they make the work life more enjoyable, work and life hours are blurred a bit more. I work on Saturday and Sunday, but that's okay because I'm never really burnt out.
The one draw back is lack of social connection while you work. I do video meetings every day and we cover the necessary items as far as the business goes, but there's definitely some fundamental human need to interact with other people and maybe form social groups or something. I used to work out of a different coffee shop a day, but working for long periods of time in semi-isolation and uncomfortable chairs isn't the heaven I imagined it to be. Whether you're working in office or out of office, finding people you enjoy working around I think is important. Then again I'm more an extrovert so maybe reclusive individuals won't feel the same way.
Lastly, free time:
I did travel around the world for about 8 months. I personally wasn't any less productive on my work hours, because in my mind the A.I stuff and having income was #1 priority, travel #2. It's a bit stressful to find a place to work with great wifi when you change cities every week.
Maybe this is obvious, but working every day is a different experience than vacationing every day. After about 3 months you get very used to changing scenery and new places do not have the 'wow' factor, so I think most people settle in one place after traveling for a while. I settled back to Boston because of the A.I community there.
Lastly, if I had to redo the experience, I would have started with a more specific outline of what I wanted to accomplish with my extra time. Other than that everything has been wonderful.
Any questions, feel free to ask! This is the first time I've written about my experience woo hoo!