1. Create a Date Parameter.
 

2. Create "Custom Date"  fields for year/month/day.

3. Create a calculated field.

• name: TS_order_date
• formula: 
  IF [date type]=1 THEN [Order Date (Years)]
  ELSEIF [date type]=2 THEN [Order Date (Months)]
  ELSEIF [date type]=3 THEN [Order Date (Days)]
  END

4. Create a calculated field.

• name: TS_count(orders)
• formula:

COUNT([Orders])/COUNTD([Order Date])

5. Drag the [TS_order_date] to the column and set it as discrete, and drag [TS_count(orders)] to the row.

 
6. Right-click the [date type] parameter and select [show parameter]. Select different values to check the results.
 
See the attached workbook.