Calibre will automatically create Snapshots (a series of tests) at allocated intervals. You can change the scheduler to your needs when adding a new Site or later on on the Site → Settings → Test Agent page:
The options are:
Off: the scheduler will not run for this Site. This is useful if you’re creating regular Snapshots following deployments or as part of a continuous integration suite.
Daily, at a given hour: Snapshots will be created at a chosen hour, every day.
Hourly: Snapshots will be created every hour of the day.
Every X Hours: Snapshots will be created every ’x’ number of hours.