-- "DT" is an abbreviation for "DATETIME", not "DATE"
DECLARE @StartDT DATETIME
,@EndDT DATETIME
;
SELECT @StartDT = '2000-01-01 10:30:50.780'
,@EndDT = '2000-01-02 12:34:56.789'
;
--===== Display the dates and the duration
SELECT StartDT = @StartDT
,EndDT = @EndDT
,Duration = @EndDT-@StartDT
;