You can start & stop (Publish/Unpublish) an automation at any time. You can also set the automation to start or stop on a certain date/time.
Select a campaign and open it up to edit it. On the right side you will see “Publish at (date/time)” and “Unpublish at (date/time”. Here you can type the date of when you want your campaign to publish (or unpublish) which will be when your automation starts (or stops).