You can use this simple DATEDIFF function to calculate the difference, in seconds, between a SubmitDate and CompleteDate.
SELECT DATEDIFF(s, SubmitDate,CompleteDate)
FROM Table
WHERE Column1=ID Value
This will allow you to use the result from above (seconds) to convert the seconds into HH:MM format.
DECLARE @NumberOfSeconds INT
SET @NumberOfSeconds = Result from above
SELECT CAST(@NumberOfSeconds / 3600 AS VARCHAR(3)) + ':' +
RIGHT('0' + CAST(@NumberOfSeconds % 3600 / 60 AS VARCHAR(2)), 2)
