By February 2009, any Landsat archive scene selected by a user will be processed, at no charge, automatically to a standard product recipe and staged for electronic retrieval. In addition, newly acquired scenes meeting a cloud cover threshold of 20% or below will be processed to the standard recipe and placed on line for at least three months, after which they will remain available for selection from the archive. Details can be found in the USGS Technical Announcement.

Source:
USGS Technical Announcement