Though I am not in your position, as a freelance ATPL theory instructor I see and talk to students in the same predicament nearly every week.
Everybody is different when it comes to learning so if mornings best for you (& me) then continue down this route, when I did my training many years ago I always took a full day off per week as you can get information overload.
Students make the mistake of just reading the material, this is not good enough and you need to HAND write notes and key facts. Eg definition of great circles and rhumb lines. I also suggest you get some cue cards and write down all the various formulas separated by subject. Eg. distance/speed/time, convergence etc.
Students certainly have quit their jobs to either do more D/L or switch to full-time courses but not everybody can do this though. Your 20 hours sounds more than enough providing you are taking it all in and passing the progress tests.
D/L is not an easy option and requires time, commitment with no distractions and full support to achieve results and as you say can be an exhausting, lonely uphill battle. Regretfully those students who are missing any of these elements - however well intended they might be are likely to be taking two/three attempts for a subject and/or running out of time (18 months) and having to start again.
Hope that helps.