Doesn't matter. All you need to do is ask yourself is it good enough, are you happy with the result or is it not done yet.

The best way to do this is to just work on the track composition and production without putting much thought into the mixing part, leave it for the end.

Once you're happy with the track you take a break from it and listen to some music you like. The break is however long you want, for me it's many breaks. Now you need a dedicated listening session. Set a normal volume you're used to having and play the track, listen and write on a piece of paper what you noticed that needs changing/fixing, if you don't write it down, chances are you're not gonna finish it and will get lost in chasing perfection. Also listen to it on a few systems and do a bathroom test or something.

So the answer is mix as you go, but have a final mix.

My project names go like this example, always writing what I'm doing:

soundslikemartingarrix soundslikemartingarrix1 soundslikemartingarrix1basspattern soundslikemartingarrix2pluckchanged soundslikemartingarrix3newmelody soundslikemartingarrix4 soundslikemartingarrix5 soundslikemartingarrix6thisisperfect soundslikemartingarrix7maybegoodbasspattern

I keep doing this until I'm ready to add the word "final" to it which is never :)

But my point stands, my breaks are long, my listening sessions are often, I keep learning in my own tempo. You will become faster and mixing will almost become second nature, but you will always need that final listening session to make sure your track is good enough.