Bit of a waste of time. Youll be going over most of it in class. Do all your classwork, compile notes in class and then consolidate your learning of the concepts after youve done it in class.
What im doing is revising what we did in the last lesson and reading over what we will be doing in the next lesson.
Well its not like im dedicating like hours on end to it. If I do like 1-1.5 hours a day I can get the text book done like half way through the year.
Youre dedicating 125(?) hours to it. You'll be doing the same thing in class. Youre better off summarising during and after class, then reading over the next class, so when it comes to that next class youve got queries you can bring up and some prior understanding. You dont know the course or how to apply the study design anywhere near as well as your teacher will, so you might distribute all your effort towards areas of the course which dont need to be explored in depth, and in turn a diluted understanding of higher weighted areas of the course.
Its all about studying effectively. Pointlessly making work for yourself is not as helpful as it may seem.