SQL Timezone difference

I'm trying to make a block that will display the users that have contributed points this month by calling:

SELECT u.uid, u.name, u.picture, SUM(t.points) as period_points FROM userpoints_txn t
INNER JOIN users u ON u.uid = t.uid
WHERE DATE(FROM_UNIXTIME(t.time_stamp) ) > DATE_SUB(CURDATE(), interval DAY(curdate()) day)
GROUP BY u.uid
ORDER BY SUM(`points`) DESC

The problem is the block when displayed in any Admin screen displays the correct points based on my timezone (NZ), whereas the block when displayed on a content node displays the points based on GMT timezone.
Why are they different?