Refer this i
Declare @Time int,@LoginTime datetime = '2013-10-02 23:00:00',@LogoutTime datetime = '2013-10-03 01:08:00'
Set @Time = DATEDIFF(Minute,@LoginTime,@LogoutTime)
SELECT CAST( @Time/60 AS VARCHAR(5))+ ' Hrs' + ':'+ RIGHT('0' + CAST( @Time%60 AS VARCHAR(2)), 2)+' Min' AS 'WorkingTime'