Music, you shouldn't have to alter your FAFSA data because of a job begun after 2009-- FAFSA, I believe, is only concerned with what your fiscal circumstances were in 2009. If you need to change it for other reasons, though, you can "make corrections" to it (see FAFSA.gov--> #3 "FAFSA follow-up"). Some schools, however, may prefer that you to make that correction on their school-specific forms.
I'm getting antsy to send in my financial aid stuff... I'm still waiting on W-2 stuff. Boo waiting. But from my past experience, I'd say: the earlier the better. All of the financial service admins I have ever spoken with have confirmed this mantra, too.