I recently ran into a feature / bug / something while delaying audio for an application with sox. The delay effect appears to only delay a maximum of 3 seconds. Hopefully this will save someone else from scratching their head.

To delay audio use the pad effect:

sox file_in file_out pad begin_offset end_offset

begin_offset = seconds of silence (delay) to add to the beginning of file_out
end_offset = seconds of silence to add to the end of file_out

hope this helps
sid