How long can an underwriting message be?

PBS national corporate sponsorship messages are generally fifteen seconds long.  (In some cases they are less, depending on the number of sponsors, relative value of sponsorship, and other factors.)  National “Premier” sponsorships, acknowledged with thirty-second messages, are available only for the top category of funders.  Premier sponsorships are not available for children’s programs.  The FCC has never set an upper limit on credit length but has warned that the longer it takes to identify an underwriter, the more likely it is to be promotional.