If I’m looking for extra credit for my college application of I’m applying early decision, would I be able to take the SAT II in December then send it in later?
If what you are asking is whether a Dec SAT II test score will reach the college in time to be considered when applying early decision (ED), the answer is no for most colleges with early decision because they release decisons in mid-Dec and your scores cannot get there in time to be considered. There are some colleges that have later ED programs including ED 2 where decisons are not released until Jan or even Feb and for those there is some chance it may arrive on time if you identify the college in your test registration as one to receive scores upon release (the fastest form of delivery but you are sending the score before you know what it is). However, even that would depend on the college because they may have the Nov test date as last one that can be submitted.