Real time updates are triggered by Trello whenever certain actions occur. For example, when you create a board Trello sends an update to Punchtime informing it of the new board. While most actions on Trello trigger immediate updates, not all actions do. Most notably, changes to your profile (changing your name or avatar, for example) will not trigger an immediate update. This also means that these changes can take several hours to appear on Punchtime.
Period synchronization runs several times a day and ensures data integrity. This is a complete synchronization of your Trello boards.