To add a calendar interval global filter to a dashboard, select "Add Element" and then choose "Calendar Interval."
Selecting "Calendar Interval" from the "Add Element" pick-list will display a modal for defining the interval. To create, enter a name and then assign the default start and end dates.
How to restrict query results with this filter: In chart definition page, drag the desired date field into the "Filters" box and select the appropriate modifier (e.g. Between, Later Than, Earlier Than, etc). Using the two drop-down selectors, pick the Start and End values for the recently created Calendar Interval.