From my experience, the junior year's summer is the perfect time to start making the list.
-You would have a general idea of your GPA, since it won't change that much.
-You would be able to apply EA/ED y-ou would have a lot of time to write the essays.
I would also recommend making your list during your junior year. In doing so, you will have the time to visit the campus, look at finances, majors, and extracurriculars. Once you have a general list, which you can actually create here on CollegeVine or College Board, you should compile a list of questions and start brainstorming your essays. The essay brainstorming should likely happen during the summer between your junior and senior year. Don't start last minute because it really becomes stressful as I made the same mistake. Hope this helps.
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