Timeline:
AMCAS opens up on May 1st
- Able to create LOR entries on AMCAS and print out LOR form to provide to letter service at school or individual letter writers
- LOR can be sent to AMCAS anytime from day 1 of AMCAS opening to the end of the application cycle
- You have a choice of assigning these LORs to each school you add on AMCAS
AMCAS submit date on June 5th
- You may leave all schools unassigned to any letter on your file, and can add anytime before or after submitting
Secondaries request LORs
- Re-open AMCAS and assign the required LORs to that school and resubmit AMCAS if you did not previously assign (takes 2 minutes)
My advice would be to assign all your schools the letters you want them to get ahead of time so its one less thing you have to worry about. The letters will only get to them when they choose to upload it off the server. Exception would be some UC schools like UCSF or UCLA which I believe specify that they might not want your letters until you get a secondary since they are screened. Also Mayo traditionally sends a LOR request if they are interested in you, but you can presend them the letters and they will only upload it if you get to that point so it makes no difference.