Tiles can either use the overall page timeframe or they can have a specific tile timeframe specified in each tile configuration.
Within each tile configuration you can choose either use page timeframe or specific timeframe. The default is set to use page timeframe.
The page timeframe is the timeframe which users viewing the page can change on the fly. The default timeframe is 12 hours, as shown by the 12 hours button at the top of the page. Users can then change the timeframe by clicking on the 12 hours button. All tiles on the page which are set to use page timeframe will change to show data for the newly selected timeframe. Any tiles set to use specific timeframe will remain set to the timeframe specified when the tile was configured.
Use the setting use page timeframe if you are happy for this tile to default to 12 hours and for users to change the overall page timeframe as they need.
Use the setting specific timeframe for this tile if you wish to fix the time period displayed. For example, if you are creating a page to display several tiles for a 30 day time period, or if you wish to have several tiles showing different time periods for comparison, such as 7 days, 30 days and 3 months.