Setting the exact time Debian 6

# apt-get install ntpdate
# dpkg-reconfigure tzdata

Synchronise with time server:
# ntpdate pool.ntp.org

If all done good, then you will see the correct current time corresponding to your time zone in the screen.

To live with out manual correction of the time, the last command can be put in the /etc/crontab to update rate, for example once a week.

42 4    * * 0   root    /usr/sbin/ntpdate pool.ntp.org

Will run every Sunday at 4:42 am