That is a good and extremely relevant question, @The_Baron; not least because we all don’t have oodles of time to practice…
For inexperienced players, I’d say finish Josh’s course first before doing too much else. I am convinced @JoshFossgreen put a lot of thought into how he structured his course and how to introduce (or leave out for now) certain aspects of bass playing, music theory, harmonic knowledge etc. That said, I got inspired by a lot of the stuff in the course and then went and did some more research on aspects I wanted to know more about. Still, I finished the entire course before I sat down and thought more in-depth about what I probably should focus on now.
I would definitely suggest learning arpeggios and use perhaps 2/3 of the time you have available on that. That sounds really boring, but I think the benefits are manifold.
Arpeggios will teach you about how (common) chords are constructed, about harmonic relationships, they help you learn your fretboard (still struggling with that!), they give you shapes/boxes on the fretboard for major and minor (and major/minor/dominant 7th) arpeggios, which are the basis for most basslines you might want to construct, or for soloing at some point. Also, there are tons of variations how to practice arpeggios (just one example: upwards with the C major 7 arpeggio and from there downwards the D minor 7 arpeggio, up the E minor 7 and down the F major 7, then up the G dominant 7 and down the A minor 7 and finally up the B diminished 7 and down the C major 7 again (but one octave up from where you started)). These are, of course, the diatonic arpeggios of the C major scale. Once you can play these, there are 11 other keys to try out, and thereafter other scales as well…
Finally, you can practice arpeggios with different tempi and rhythms (accents), thus working on your timing and rhythm at the same time (always using a metronome, of course!).
So, this could make up 2/3 of your practice time (and, btw, you have to practice one group of arpeggios (like the C major diatonic arpeggios) for a few weeks at a time, to get the shapes into your muscle memory, to build up the knowledge of the notes on the fretboards, and to get the sound of these arpeggios into your ears). The remainder of your practice time, I would spend on practicing tunes and learning new ones and having fun with that. This way, you can improve your feel for grooves and learn from what other bass players have done before you.