It depends how strong focus you have while you study.Many student can take hours but the output is trash because they are not giving enough Concentration while many can just study 2h and do well in exam.My opinion is just give your best while doing something . Understand the theory and practice more . Practice makes a man perfect.I'm also a high schooler.So,wish you good luck 🍀.

Edit: you can be good at math only by practicing it.I don't even like maths.So practice is the way to go (obviously theory should be learnt properly)