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1. Select the appropriate time zone from the /usr/share/zoneinfo directory. Time zone names are relative to that directory. In this case, we will select "America/Denver"

2. Edit the /etc/sysconfig/clock text file so that it looks like this:

ZONE="America/Denver"
UTC=true
ARC=false

Of course, this assumes that your hardware clock is running UTC time...

3. Delete the following file: /etc/localtime

4. Create a new soft link for /etc/localtime. Here is an example of step 3 and step 4:

# cd /etc
# ls -al localtime
lrwxrwxrwx 1 root root 39 Mar 28 07:00 localtime -> /usr/share/zoneinfo/America/Los_Angeles

# rm /etc/localtime

# ln -s /usr/share/zoneinfo/America/Denver /etc/localtime
# ls -al localtime
lrwxrwxrwx 1 root root 34 Mar 28 08:59 localtime -> /usr/share/zoneinfo/America/Denver

# date
Fri Mar 28 09:00:04 MST 2003

Fonte : Van Emery (http://www.vanemery.com/Linux/RH-Linux-Time.html)