So having an immense amount of free time over break I find myself practicing upwards of 7 hours a day....
Well, it depends. Do you want to be really good and do you enjoy it? If so, don't listen to all the jealous detractors. Nobody ever became a great pianist by limiting themselves. This modern idea of worrying about fatigue is false, why? Because you need fatigue to get stronger. Mozart impovised for four hours at a stretch when he was like 5 years old. I remember Richter's wife saying he played for 13 hours a day. What they have in common is that they are both legends.
If you are being honest you really need to get some other hobbies, too much of anything is not healthy. There is a whole world out there using all your time to play piano seems silly.
This.
... I really, deeply enjoy it, to the point where a passage that I'm not getting right will get under my skin and I'll practice it repetitively and look up to find that I've spent 45 minutes on the same few measures.
If these measures have hundreds of notes I can maybe understand but pretty much if you find yourself working on a few bars for this long you are working on something too difficult and I feel working quite inefficiently (which over time can really hurt potential).
So having an immense amount of free time over break I find myself practicing upwards of 7 hours a day. I know that there is certainly such a thing as too much practice, where risk of injury and muscle fatigue can combine to make the extra time nearly pointless. I've heard a lot of numbers thrown around, from 4 to 6 to 8 hours max, to the statement that it's never too much. I don't play if it hurts to do so, and I take breaks but I want to make sure that I limit my risk of injury, especially as I get into some more labor intensive etudes. What is too much practice for you? What advice are you given by your teachers? How do you arrange your practice time?
2) The point, as accurately posted before, is that perfect practice makes effective practice. Like more before you, the notion that more is better is a ("Conservatory Method") gigantic level of BS. You eventually get burned out, as did a Juilliard student by the name of Van Cliburn, who went down this very same path.3) As a young man, he spent upwards of 13 hours a day practicing. As an adult, he could not even do one third that much, as evidenced by his noticeably small solo performance repertoire. Even worse, his concerto repertoire was reduced to just two pieces, the Tchaikovsky and the Rachmaninoff.
When you're feeling tired you should stop.