Electronic Advanced Passenger Information System 

You must submit an eAPIS electronic request to depart and return to the U.S. (including Puerto Rico unless flying from/to the U.S. non-stop).  Once enrolled in the system, this requirement is fairly easy to complete (Hint - enter all passenger info as "crew."  The system saves crew info but not passenger info).  Click here to LOGIN or ENROLL. 

Submit the manifest at least one hour before departing the U.S. and one hour before departing a foreign airport to return to the U.S.  There are no viable exceptions.  Unavailability of internet connections on a remote island requires that you to land at another foreign airport to submit the eAPIS.  So SUBMIT your return manifest BEFORE you depart the U.S. (Hint - if the return date is uncertain, submit multiple requests, for example, one each for Tuesday, Wednesday and Thursday.)

The manifest can be submitted as far in advance as you like (days, weeks, months).   A change to the passenger list requires a resubmission (Hint - file multiple requests with different passenger manifests if you are not certain).  A change in the arrival time and/or arrival airport can be amended with FSS via radio.  It is still a good idea, however, to call customs and alert them to your arrival.