When you make changes to any item not associated with workflow, Sitecore adds the item to an internal publishing queue.

When an item associated with workflow reaches a final workflow state, Sitecore adds it to the publishing queue. Publishing operations publish all items in the queue, copying the appropriate versions of the appropriate items from the content authoring to the content delivery (public-facing) server.

Publishing schedule

Sitecore publishes content every two hours between 6 a.m. and 6 p.m. daily.