After staring at it some more, I'd suggest perhaps switching places between the day of month and month of year circles. That way you would have consistently smaller unit of time=smaller circle.
Yeah, this screamed US date format to me! (Though there's no year in this clock)
That makes sense. I'm least happy with the (day-in-)month circle, but felt the calendar portion wasn't really useful without handling it somehow.
I wanted the year circle to evoke Earth's orbit, so it had to be near the Sun. Inserting another circle was breaking that intuition (already stretched, tbh) for me. I was flip-flopping between these two and finally decided on the current solution.
I'm even more unhappy[0] with the fact that the number of ticks and speed on that circle changes every month, depending on the calendar month duration. For a world clock, on month changes it also means that you can't represent the date correctly for all shown timezones.
I could have used some real-world phenomena that are close to our calendar month instead[1], as pointed out by another commenter. This would make it "more correct" but "less useful in everyday situations". Even though I don't plan to use it every day, one of the goals of the project was for it to aspire to being useful.
[0] unhappy is a strong word; I mean I'm not satisfied with the solution, but was unable to find one I feel better about [1] https://en.wikipedia.org/wiki/Lunar_month#Types