Not all colleges require you to submit standardized test scores. Notably, in California, both the California State University and University of California systems are test-blind, meaning they will not even look if you send them a test score. During the Covid-19 pandemic, many universities stopped requiring standardized tests, but quite a few are now once again requiring them. This trend is expected to continue as colleges look for ways to ensure their incoming students are prepared for the rigor of higher education.
Ideally, your student should be confident with their SAT score by the end of their junior year. There are fall test dates, but with everything else involved in the college application process, this just adds a lot of extra stress. Most students retake the test once or twice before they are happy with their score. With this in mind, I recommend beginning SAT prep during the summer after sophomore year or after the PSAT in fall of junior year.