Declare @create_date datetime = '1/1/2013', @execution_date DATETIME = GETDATE();
SELECT CAST(@execution_date - @create_date AS REAL)

DECLARE	@table TABLE
(
	ID		INT,
	StartDate	DATETIME,
	EndDate		DATETIME
)

INSERT	@table( ID, StartDate, EndDate )
SELECT	1, '2013-02-17 10:33:10', '2013-02-17 20:14:40' UNION ALL
SELECT	1, '2013-02-13 12:42:55', '2013-02-14 14:30:50' UNION ALL
SELECT	1, '2013-02-12 15:04:32', '2013-02-15 12:22:25' UNION ALL
SELECT	1, '2013-02-16 20:08:18', '2013-02-18 02:10:10'

SELECT	T.ID, T.StartDate, T.EndDate,
	CASE
		WHEN DATEADD( DAY, DATEDIFF( DAY, T.StartDate, T.EndDate ), T.StartDate ) <= T.EndDate
		THEN DATEDIFF( DAY, T.StartDate, T.EndDate )
		ELSE DATEDIFF( DAY, T.StartDate, T.EndDate ) - 1
	END + --====================Gives you the days
	(
		CASE
			WHEN DATEADD( MINUTE, DATEDIFF( MINUTE, T.StartDate, T.EndDate ), T.StartDate ) <= T.EndDate
			THEN DATEDIFF( MINUTE, T.StartDate, T.EndDate )
			ELSE DATEDIFF( MINUTE, T.StartDate, T.EndDate ) - 1
		END % ( 60 * 24 )
	) / 1440.00 AS Result --===============Gives you the hours in decimals
FROM	@table AS T