After you have set up an account with them and entered in the schools that you have attended, then you can print a transcript matching form. You can send this in as soon as you want. They told me that they have a file for each applicant where things (LOR, transcripts) are held until you submit your application after which they start processing the whole thing. I'd send it in now if I were you.
You probably could, but personally I wouldn't. We have all heard the horror stories about AADSAS and their organization. I recommend sending the transcripts after you submit your application. If you already have them on hand, express mail them. At least this eliminates one potential screw-up from AADSAS.