Be very very careful of studying beyond the level you think is comfortable. My experience has been that you cannot push yourself to learn difficult things, especially math, faster than a certain pace. Sure, your limit may be 20% higher than what you think it is, but it's not 200% higher. Spending more time on a task when you just don't feel up to it is useless, because instead of thinking you'll just be spending more time staring at the page and having your mind drift off.

I've found that the various methods of 'productivity boosting' (pomodoros, etc) are largely useless and do one of two things: Either decrease your productivity, or momentarily increase it at the expense of a huge decrease later on (anything from 'feeling fuzzy for a couple of days' to 'total burnout for 3 weeks'). Unless you have a mental illness, your brain is already a finely-tuned machine for learning and doing. Don't fool yourself into thinking you can improve it just by some clever schedule rearrangement.

The point to all of this is that you should refrain from 'planning ahead' when it comes to learning. Sure, you should have some general overall sketch of what you want to learn, but at each particular moment in time, the best strategy is to simply pick some topic and try to learn it as best you can, until you get tired. Then rest until you feel you can go at it again. And avoid internet distractions that use up your mental energy but don't cause you to learn anything.

One of my professors once mentioned that there's an upper limit to how much learning you can do in a sleep cycle [citation needed]. This is congruent with my experience, both before and after he mentioned that, so I tend to believe it. Personally, I tend to max out around 3-4 hours, so the times you're talking about seem reasonable. If you can restructure your work times, napping is a good strategy; I've talked to a few people who report getting through grad school by napping once they'd saturated their brain's capacity to learn new stuff.

Interleaved practice is good. This study had subjects practice finding the volume of unconventional geometric solids. One group clustered their practice; they found the volumes of a bunch of wedges, then a bunch of spheroids, etc. The other group had their practice problems mixed. On a final test, the former group got 20% right, and the latter group got 63% right. citation.

What this suggests is you should perhaps study programming and algebra at the same time, switching between the two fairly frequently. It feels like you're going slower, but, as the authors of the book emphasize, you're trading the illusion of learning for more durable learning.

The AoPS textbooks are really, really good. In fact, I'm pretty sure they're the only good algebra textbooks you're going to find, unless you count abstract or linear algebra; most textbooks at that level are mediocre. As luke_prog has mentioned, good textbooks are the usually the quickest and best way to learn new material. Quality learning takes time, and you're doing yourself no favors by spending that time looking for faster alternatives.