I can't speak much for "Mambo" (..which means I probably shouldn't be postig here) but there is an overall "fix" for timezone woes. In your .htaccess file you can slap in a line that reads:
SetEnv TZ America/New_York
..where you'd change the "America/New_York" to either "Pacific/Aukland" or "Pacific/Chatham" (..dunno specifically where ya are, but you get the idea).
Note that if you're running this from shell or in crontab, you'll need to edit your .profile or crontab input file to include a line that reads:
to properly implement the timezone for stuff at the OS level - the .htaccess setting is purely for the Apache daemon.