DateDiff( )函式，請教參數設定。(編號：247)

Function DateDiff(Interval As String, Date1, Date2, [FirstDayOfWeek As VbDayOfWeek = vbSunday], [FirstWeekOfYear As VbFirstWeekOfYear = vbFirstJan1])
其中Interval As String如何設定。Date1, Date2給的值"88/12/10"
是否正確。