You can schedule content export to run at a regular frequency (labelled Recurring Export). The default value is 24 hours, starting at 23:59:59 UTC. When programming your download process, please wait for the job to complete before retrieving the file.
You can also export content manually (labelled Ad-hoc Export) based on a date range, but it should not be run at the same time as a recurring export. The ad hoc export will contain data from 00:00:00 to 23:59:59 GMT on the selected dates.
For more information on the ad hoc or scheduled content exports, please refer to the Admin Guide.