I attached a workbook that goes through some of the details. Long story short, it's probably best to use a standard date field than hard code one, but depending on your needs both are possible. To hardcode simply go to 'Analysis' > 'Create Calculated Field' and then type the string you would like to appear in quotes
This will then be a string value you can use on your worksheets.
For the sake of clarity and data quality, however, I suggest that if you have a date field in your data that it should be used. The instructions for customizing it are in the attached workbook. Good luck!
DAQuarter.twbx 1,005.9 KB