Question

Goal:
To display data with this list:

Hour  
-----
2
2,5
1

Problem:
Is it any possibiltiy to convert column StartTime and EndTime into specific datatype and then doing a calculacution of X1- X2

CREATE TABLE Data
(   
    StartTime VARCHAR(5), 
    EndTime VARCHAR(5), 
)   
GO

INSERT INTO Data(StartTime,EndTime)   
SELECT '10:00','12:00' UNION ALL
SELECT '13:30','16:00' UNION ALL
SELECT '14:00','15:00' UNION ALL
GO

Answer 1

EDITED: To get mins in decimals

SELECT ROUND(CAST( Mins AS FLOAT)/60,2) AS [hour]
FROM (
SELECT DATEDIFF(minute, CAST(StartTime AS TIME),CAST(EndTime AS TIME)) AS Mins 
    FROM  Data
) A