sarbarah2: I get the impression that you may perhaps be **too** focused on what seems right to you and what your personal priorities are, and not sufficiently focused on what God’s priorities for you are.
Chazal tell us “meimis atzmo l’Torah” – kill yourself for Torah. This can be understood in many, many ways, but one interpretation is that our greatest task in life it to truly subjugate ourselves to the Torah’s demands on us. We need to conquer our own will and our own value judgments and replace them with God’s will and God’s value judgments.
You may sincerely believe that davening shemona esrei for an hour several times a day “is one of the most important things” you do. But is it? What does the Torah say? Is davening for several hours a day instead of for a more typical length of time really more important than attending your classes on time? What about when it comes time for you to get a job; will davening a one hour shemona esrrei be more important than getting to work on time as your employer expects? Whether or not it is right to rely on siyata d’shmaya (which one poster mentioned, but which, as was pointed out, was reserved for the chassidim rishonim) is not really the question. Even if you had the right to rely on God to make it all right because you daven so well and long, is that really what the Torah expects of you?
I am not trying to answer one way or the other. My point is simply that you seem a bit too set in your ways. You seem to be looking for justifications for your practice and unwilling to consider whether what you are doing and the way it is affecting your other obligations is really the right thing to do. Please, talk to a rav, or someone else that you trust to give you an accurate portrayal of what the halacha expects from you here – not just what will feel good. Explain the situation – your desire to daven long, the affect it has on your schooling, the tension it will likely cause between you, your teachers, the school administration, and your parents. See what he/she says.