You can use the function datediff, which works with 3 parameters – Interval type (minutes, hours, days, etc') Start time and end time. For example
Select datediff(mi,'20130612 10:00:00', '20130612 11:00:00')
Select datediff(hour,'20130612 10:00:00', '20130612 11:00:00')
Adi
--------------------------------------------------------------
To know how to ask questions and increase the chances of getting asnwers:
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/