GPG validation failed

/etc/cron.daily/spamassassin was unhappy for some time now: error: GPG validation failed! The update downloaded successfully, but the GPG signature verificationfailed. channel: GPG validation failed, channel failed Apparently GnuPG checks for cross-certification now, hence the error message. Here is how to solve it:
sa-update --import GPG.KEY
Oh, and can somebody explain to me, what this sleep(1) thingy in /etc/cron.daily/spamassassin is about? What's it used for?