Consulta para converter Varchar HH:MM em minutos inteiros no SQL Server 2008

SELECT LTRIM(DATEDIFF(MINUTE, 0, TimeSpent)) 
  FROM yourtable

| TIMESPENT |
-------------
|     00:12 |
|     01:05 |
|     10:00 |

| MINUTES |
-----------
|      12 |
|      65 |
|     600 |