When clicked on the Secondary Questions tab, in the paragraph about letters of rec it says this:
"I. Letters of Recommendation
It is the applicant's responsibility to see that the application is complete, the non-refundable $80 application fee is paid, and the required letters of recommendation received.
Letters of recommendation are to be transmitted via AMCAS only. Please review with AMCAS their letter transmission policy at
www.aamc.org/students/amcas. Do not submit letters of recommendation to Sidney Kimmel Medical College.
To activate your application, please complete and return this form with your activation fee within two (2)weeks."
Unless I'm misunderstanding the statement, I take that as having two weeks to complete the secondary from the time you receive it.