Това трябва да направи:
;WITH CTE AS
(
SELECT *,
DATEADD(HOUR,DOCTIME/100,DOCDATE) DocDateHour,
CAST(RIGHT(DOCTIME,2) AS INT) DocTimeOnly
FROM OPOR
)
SELECT DATEADD(MINUTE,DocTimeOnly,DocDateHour)
FROM CTE
И тук е модифицираният sqlfiddle за да опитате.