Colleges have different preferences with regards to submitting testing scores. Some colleges will keep scores for a short time to match with additional application materials; some, however, prefer to have your application before they receive a score report. Both the College Board which offers the SAT I and SAT subject tests and the ACT test center will allow you to submit scores at any point after they are available.
For simplicity's sake I suggest that you hold off on sending scores in until all your applications have been submitted, that way you don't have to keep track of those you have sent in advance and those you haven't.