Data-mining company AdKnowledge Inc. said Monday that business marketers get the most bang for their buck during lunch hours Mondays, Tuesdays and Wednesdays. Also, click-through rates aren't all they are cracked up to be. In its first-quarter advertising report, AdKnowledge, Palo Alto, Calif., said people who view an Internet advertisement but fail to go directly to a site are not entirely dead leads. In fact, in cases when people later returned to an advertiser's site, they were one-third more likely to complete a purchase or registration. AdKnowledge makes the argument that marketers should not discount these visits when calculating the return on investment for a campaign. In addition, the company said advertising click-through rates are 38% higher on the first three days of a working week than they are on Saturdays. AdKnowledge is the marketing analysis arm of Engage Technologies Inc.