Your application will need to be properly configured before the scheduling controls appear on the page. If you do not see them, please contact CSS Support.
There are two types of time period in the Repeat Type: Every TimePeriod and Alert TimePeriod. Every will run the report every specified time period, and produce an export even if there are no results to display. This means that you may get a scheduled report email with no results, if there are no results to be displayed. Alert will run the report but only email output to specified recipients if there are results - a report which returns 0 records will not send anything to recipients.