The DATEDIFF function is your friend here

😎

SELECT

isLocked

,LastLockoutDate

,currentDte

,DATEDIFF(MINUTE,LastLockoutDate,currentDte) AS DIFF_MINUTE

FROM @tAccount

Result

isLocked LastLockoutDate currentDte DIFF_MINUTE

-------- ----------------------- ----------------------- -----------

1 2014-04-26 16:11:25.337 2014-04-26 18:57:15.777 166