i checked amcas and couldn't find the answer....

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.
Get help with your application

Use all the free resources available to you from SDN: articles, guides, expert advising, forums discussions, and school research.

You can send letters to AMCAS as soon as it opens I believe. However, schools that use these service (at least this cycle) were few and far between. A good rule of thumb would be to have your letters ready to be sent (i.e. through Interfolio) by the time you submit your primary AMCAS - some schools will get back to you very fast (like GW) and you shouldn't have to wait to fill out their application due to a delay in your letters!