Many do not say by when AP scores must be submitted but there is usually an expectation that you do so before the semester begins, typically by end of July, including so the college can verify that you can take a course you may have enrolled in that requires completion of the course for which you need AP credit. However, there are exceptions out there, including the UCs, which require AP scores to be submitted by July 15, see http://admission.universityofcalifornia.edu/how-to-apply/after-you-apply/index.html
Thus, you should check with the college to which you are admitted. The score, typically a 3, 4,or 5, needed to get college credit depends on the applicable course and the particular college.