The article How to know if the Auto Date table is adequate when using Power BI provides a look into the inner workings of how Microsoft Power BI handles dates and times.

Microsoft's Power BI supplies a default date table that’s adequate for many time grouping requirements. Find out how to know if the Auto date table is adequate when using Power BI.

Microsoft's updated Power BI 2.0 business-intelligence service will be generally available worldwide starting July 24.