The auto backup feature uses the native wordpress cron functionality.
This doesn't work exactly like a normal cron process you might normally use in a UNIX environment.
The plugin will attempt to do hourly checks for any scheduled cron processes based on the "aiowps_hourly_cron_event" hook which is set when the plugin is activated.
So in your case, if you activated the plugin at 13:00 (your local time) and you configured the auto DB backup settings to do once daily backups, the plugin will theoretically* do the backups at 13:00 daily.
* I say theoretically, because the way in which the WP cron functionality works is that in order for the scheduled job to fire at the expected time, you will need to have some kind of activity on your site around the same time to trigger the processes. By activity I mean either people visiting your site on front end or backend.
The more your site has a regular constant traffic stream the more reliably consistent the WP cron will work.