I'm in the first 4 months of my PhD in Music and so far I think I've been fairly productive despite having a wet blanket for a supervisor. The relationship is improving but I have mixed feelings on it.
I've gotten a fair amount of writing and reading done but lately there are days where I do absolutely nothing productive.

I had imagined myself taking so much control of my time and being productive towards several different goals in regards to reading, writing, and developing new skills in my field.

I had envisioned my thesis as being a collection of published papers which I could edit into an academic book. However lately I've been assigned the task of doing a lit review instead. I'm wondering if I could just publish a couple papers this year and nix the lit review? The lit review just feels like a hundred little book reports and I'm honestly triggered by it (memories of middle school days).

Does anyone else have 2-3 days each week where they do nothing PhD related?
I'd say most days I put in 1-3 hours of reading, 1-2 hours of writing and then music specific stuff like composition or trying to wrap my head around some of the interdisciplinary parts (programming, math etc)

I'm thinking of tracking my time with some sort of online digital journal or something just to know where I stand as maybe that would help me get a perspective on just how productive I've been. I used to despise logging time in a database when I worked in industry but maybe it would be a benefit in my PhD?

I guess my biggest problem is that my days off don't always consist of Sat-Sun. Some weeks it's Tues and Fri or some other random combo and this throws me off too.

Any thoughts/suggestions appreciated!

Judging your productivity by time worked is not a good idea.
It's far better to set goals and keep an "achievements" book to help you remember how much you are doing.
List everything you do which pushes you along the path to your PhD award. As time goes by the granularity of your achievements should increase. I would record a note every time you finish a chapter or a full book for example.

Agreed... measuring productivity by time is pretty unhelpful (though totally normalised in society). I wonder if you'd benefit from making a bullet list every morning (or night before) with maybe 5 tasks you'd like to get done that day to move your project forward, and try and get through as much of them as possible! :)

Also it's important to have days where you don't do any work at all so that you don't burn out, doesn't matter if it's not weekend if that suits you better