It appears that my web host (SourceForge) has the classic WP-Cron issue where the web server cannot resolve its own URL, a capability which WP-Cron requires to function. I set up a real cron job on a server of my own to periodically tickle WP-Cron remotely on my sourceforge site. That has got WP-Cron working properly and Cyan Backup along with it.
