failed to restart hbase because of time synchronization

Missing time synchronization, scm console cannot start properly. Because of time sync, I installed ntpdate like below;

2011/10/07 - [Programming] - CentOS: time syncronization in local network / setting timezone

However time sync is broken after 2 months. So, to prohibit this problem, I wrote 'crontab' on every server.

0 0 * * * /sbin/ntpdate [ntp server] > /dev/null 2>&1