French SAT II

I’m currently a junior in IB French 3 and AP U.S. History and would like to apply ED to my top choice school. When would it be advised for me to take the SAT subject tests?

When are your IB exams in those subjects? You can sit the subject tests as early as the next test date following those, assuming that the curriculum prepares you well enough.

in May or June this year (French is not offered at each sitting so you need to check).
If you’re stronger at listening than grammar and reading, taking the November test, that includes 20% listening, can be another possibility. However you cut it close for the senior year scores.