Advice on when to prepare for the SAT / ACT?

I’m a sophomore in high school and have taken the practice SAT / ACT; I was half asleep when I did both tests and got roughly equivalent scores (scores were meh). I wanted to know when you guys plan or recommend to start full on studying for either test. I’ve been given mixed advice: studying during the school year, summer, etc and am fully aware the amount of studying varies upon your current knowledge and what score you aim for.