This guide explains the NIH Public Access Policy, the process for submitting peer-reviewed articles to PubMed Central and how to use NIH tools to manage and verify compliance.
If you have any doubt, insert the following text into the copyright tranfer document before signing: “Journal acknowledges that Author retains the right to provide a copy of the final peer-reviewed manuscript to the NIH upon acceptance for Journal publication, for public archiving in PubMed Central as soon as possible but no later than 12 months after publication by Journal.”
Source: NIH Website: http://publicaccess.nih.gov/FAQ.htm#778