The ADEA website states "Certiphi Screening sends each accepted student three e-mails regarding the criminal background check: the first e-mail is sent as soon as we are notified of your acceptance by ADEA AADSAS; if you have not logged into our system and authorized the background check after 10 days, you receive a second e-mail reminding you to do so; and if you still have not logged in after 20 days, a third e-mail reminder is sent. If you opt to attend a non-participatingschool, please disregard all three e-mails, as they apply only tostudents accepted to participating ADEA AADSAS schools."
I am not sure how long they give you after the third email is sent, but you have until at least December 24th, since Certiphi sent the first email on December 4th. I am almost positive that you have longer though because I highly doubt they make you do it the same day that the third email is sent.