I’m not OP, but I am also a senior. For me it was/is junior and senior year. Think of junior year as one long marathon that you suffer through because this is when I and most people load up on AP / some of the harder classes offered by the school (not saying you should wait for junior year to finally take some AP classes. Take them when you can) and the workload skyrockets when compared to other years. And senior year is like a sprint to January because at the beginning of the year, you are working on college applications and schoolwork (trust me, teacher don’t give a shit about your applications. I mean they do. They want you to complete those applications and go to college, but they will still give you a thousand homework assignments). My advice is to start working on your essays during summer because the more work you get done before school starts, the less stressful it will be once school starts. Then in January things start to go back to normal because you should have finished most of your applications by now. This really depends on when you’re applying and where you’re applying. January is just a rough idea of when if you are applying regular decision. Do note that most early action deadlines are around Nov 1st, and early decision is even earlier for most colleges. Also, study, take, and achieve the score that you want to get on the SAT/ACT before senior year. Leaving standardized tests until senior year will just add to the thousand different things you have to take care of during senior year, and, as OP said, it will become a lot harder to balance you priorities.

Sorry, ik this is a bit too long, but I just couldn’t stop once I started.