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.