Allows you to set a custom timezone for the clock by entering the name of a file in the zoneinfo database. If left blank, the clock uses the localtime.
sudo cp -p /usr/share/zoneinfo/Europe/Rome /etc/localtime. You may have to restart xfce4. The date command uses the value of the TZ env. variable if set. If not set, it uses /etc/localtime. I noticed in the included picture the time zone name in the xfce4 time zone field is wrong. It should be Europe/Rome, not Europe/Italy/Rome since it is really a file path relative to /usr/share/zoneinfo.
ln -s /usr/share/zoneinfo/Europe/Brussels /etc/localtime
adjkerntz should be run only if you are dual booting windows (that prefers the cmos time to be localtime). But this has nothing to do with /etc/localtime. Unless you *expect* your local timezone to change (very very unlikely) cp is better as then date etc show correct time even before /usr is mounted (usually nowadays /usr is usually not a separate filesystem so it doesn’t matter whether you use cp or on -s)See FILES and BUGS tzsetup().