Incoming freshmen obviously do the CSS-Profile when applying. But what’s the typical deadline for older student to fill it out?
I don’t know if there is any “typical” deadline. Each college that requires annual financial aid forms for those upperclassmen asking for aid set their own deadlines. Check the FA web page of each school to get an idea.
Many CSS schools only require FAFSA in subsequent years. You need to check the website of each college.
Deadlines and filing requirements vary wildly.
Check your school website.