Answer
Rather than building a dedicated new schedule, piggyback your script off an existing daily scheduled task: create a Custom Event of type PL/SQL block that fires on the standard BACKGROUND_JOB_IS_PROCESSED event, filtered to trigger specifically when an existing daily task (like the Heavy Cleanup job, which typically runs once a day) completes — that gives your custom logic a reliable daily trigger without needing its own separate schedule. For the HTML requirement, call command_sys.mail directly from your PL/SQL code with your own specified content type, rather than relying on the environment's shared Mail Sender's fixed PLAIN TEXT setting — calling the mail procedure directly like this lets you send HTML-formatted content for just this specific email, independent of what the default Mail Sender is configured for.