Hi Roberto - If you are using Tableau Server there are settings in the Configure Tableau Server to refresh less frequently or refresh more frequently (real-time) when connecting to data sources. If you are only using desktop this KB article maybe helpful Disabling External Caching in Tableau Desktop and Tableau Reader | Tableau Software
It's my understanding that even with a live connection, 'something' needs to initiate a refresh.
Either F5 or a refresh via the menu will do this, there's no time based refresh. Additionally, any action which requires a query to the database which cannot be fulfilled by the cache.
Take a read of this - Tinkering with Data Refresh & Auto-Refresh « Tableau Tinkering