It sounds like if you child is applying for DE they need to apply for early entry/early decision. When does that mean applications are due? Also, given that early date, when should they take SAT/ACT? (And I’m guessing next summer will be spent writing essays and trying to squeeze in another internship!)
Typically ED decisions are due 11/1 or 11/15, but each college is different, so you need to check each one’s web page.
Testing depends on the readiness of your student.
Testing in the spring of junior year allows time to retake if you are not satisfied with your scores. You may test on two dates in the fall of senior year, however, test prep at that point (if desired or necessary) will leave you with less time for difficult classes and college applications. After a certain point, you may have to send a score report to a college before you’ve seen your score, and, while it saves time and money, many kids regret that later. Some colleges will tell you the last date upon which you may test in order to have your scores in on time.
If your student is ready, you could test this December (assuming the tests aren’t canceled) and try again in the spring. Indeed, next year could very well be another across-the-board test-optional admissions season. So there is no one single right answer. It depends how much your students wants to put into it.