Tableau has lots of useful calculations for date fields, here are a few:
Tip: Date_part can be 'day', 'week', 'month', 'quarter', 'year', 'hour', 'minute', 'second'. There is also 'dayofyear' e.g. Feb 1 is 32, and 'weekday' e.g. Monday, Tuesday. The date_part needs to be in quotation marks, lowercase, and singular e.g. not 'days'.
DATEADD
DATEDIFF
Make sure the first date is your starting date. In the sample superstore dataset, you can calculate the difference between the order date and the shipping date to calculate 'days to ship'.
DATENAME
DATEPART
