I received an email invitation to download their secondary (you have to send it via snail mail, I would use Priority Mail with Delivery Confirmation) one week after my AMCAS was verified.
you will eventually receive an email to do so but you can download and send in the secondary beforehand. just make sure you include a hardcopy of your AMCAS as instructed. last year, i forgot and spent a few extra bucks on postage.