Kentico CMS allows you to specify when the document will be published. When you edit the document form, you can typically find the Publish from/Publish to fields at the end of the form:
When you set these values, the document will be displayed on the web site only in the given time period.
If you do not set the Publish from value, the document will be displayed on the live site immediately.
If you do not set the Publish to value, the document will never expire.
Content scheduling and workflow/versioning
If you set publish from/to values to documents that use workflow, they will not be published before they are approved. However, the publishing time may not be exact since the publishing is ensured by a scheduled process that is executed every minute by default. You can check the status of this process in CMS Desk -> Administration -> Scheduled tasks -> choose the web site and search for the Content scheduling task.