1) out of the list debian ntpd installed on my machine, this one comes closest to you:
it't located in Queretaro/Mexico (says the file
2) do you use ntpdate or ntpd ? With the latter one you don't need any cronjob. If you use ntpdate you should specify more detailed what exactly you did and what went wrong.
You could just put a script into /etc/cron.daily or put the commands into rc.local to sync at startup. This should all should work fine.