The Clock applet takes the time from the system clock, which in turn, takes the time from the hardware clock. Sometimes the hardware clock does not reflect accurate time.
You can change the time for the hardware clock in the following ways:
Enter the BIOS setup and change the time directly.
Use the ntpdate command to set the time zone and synchronize the clock, as in the following example:
ntpdate -b clock.fmt.he.net.
Synchronize the hardware clock to the Unix clock, using the following command:
hwclock --systohc
You can obtain a list of Internet time servers from http://www.boulder.nist.gov/timefreq/service/time-servers.html.