Not sure exactly I understand the question, but if you are asking how often the directory is checked to insure that the links are valid and not dead (404, etc) then perhaps
Who is "Robozilla"? might be worth checking out.
I am not aware of a specific schedule if there is one for the automated system, AFAIK it is run periodically. Editors can of course run a link check manually any time they choose on the categories they are working in.
If you notice a problem area, please feel free to report it to us via the
Quality Control Thread and someone can have a look.
Hope that helps.