At Freakonomics, they're talking about an advertisement that says that the average termite eats 24 hours a day. (This is an ad for a pest control company.)
Of course, this isn't possible!
Nearly every termite is actually below average; I don't know much about termites but at some point they slack off.
However, the average termite colony might be eating close to 24 hours a day, in that at least one of the termites in your house may be eating at any given moment. And I think this is the point the ad was trying to make -- termites are constantly destroying your house. (Even this might not be true. Do termites sleep at night?)