I know the feeling. I'm also a high school student and, even though I'm not an expert in this matter, perhaps my own experience can help you.
When it's time to study maths or physics I think is normal to spend more time on reading than in other subjects. I guess it's logical: you analyze the problem, memorize formulas, recreate the problem in your mind and you try to figure out how to solve it...In my opinion is very important to make clear you comprehend the base knowledge. If you don't understand the main principles, it will be hard to understand higher problems. In fact, in my case I'm trying to rebuild and optimize my basic knowledge in Maths and Physics because I have realized that in more complex matters even when I get the concept I fail in the mathematical resolution or in simple mistakes.
Other users have said this, but I think it's importan to highlight: practice, more practice and timetables. I'm currently doing the IB course and our teachers have insisted a lot in the importance of plannifying our study. If you're studying by your own too and you want to keep a good level in both, is necessary to have this in mind.
I understand you're concerns about your leisure time and hobbies. It's difficult, but is possible to mantain a balance with your studies, your social life and your leisure time. I'd be lying if I told you that it's easy for me and I can do everything I want. However, you could follow a routine that fits you including your hobbies, studies and social life. Make it flexible. And yeah, you need sacrifices (for example, I do not use the computer from monday to sunday if it's not for scholar issues). But that depends on you.
Regarding to the reading issue:Concentration and calm: It would be awesome if we could read a entire volum in one evening, but...it's difficult. My advice is this: don't worry about how much you read, worry about how much you understand. I you read a book per day but you only remember the title...there's something wrong. If you need more time in order to comnprehend the full text, you'll spend more time. But trust me: over time it will be more gratificating. As you understand more basic concepts, you'll be more prepared for more complex texts and your reading and analysying skills will improve. Don't worry if you need more time than other students. Take your time. Just put all your will on the study and focus in the tasks. If you need squemes or drawings in order to make sure you understand the concept,s keep a notebook by your side you you can write down your conclusions or your doubts.
Our teacher told us something curious: Niels Bohr had fame for his "slowness" in comprehension during scientific gatherings. When a young scientist came and exposed his work, everyone agreed and clapped for his brilliance. Bohr needed more time to assimilate his ideas and everyone tried to explain him the work of the young scientist. Nevertheless when Bohr spoke and shared his own ideas about the scientist's work, it resulted that Bohr's conclusions were more accurated than the scientist's. Curious, huh?
Read needs its time. What is important is what does this study mean for you and how much you need for learning.