The recurring job checks, every time it runs, for active campaigns whose schedule matches today (start date reached, correct week/month interval, matching weekday or day-of-month, and end date not passed) and whose Preferred Send Time matches the current hour and minute. It then rebuilds the recipient list from the campaign's saved groups (minus its excluded groups), fills in shortkeys per person, sends each message directly and deducts the balance. Because the match is on the exact minute, the job has to run at that minute — if your site's scheduled jobs run less often than once a minute, choose a send time aligned with their schedule or ask Sprwt support. Failures are logged under History > Recurring with the error message.