How short can an underwriting announcement be?

Granted, this question isn’t frequently asked, but you should be aware that the FCC requires that underwriters be disclosed on the air at the time of the broadcast and that the disclosure be of sufficient length to be understood by the average viewer or listener.  There are to be no anonymous contributors behind a broadcast.  At PBS we usually think the minimum disclosure is three seconds.  If there are too many funders to name them all on the air in a reasonable length of time, the on-air announcement will refer viewers to the complete list of funders available from PBS or from the producer.